1. imports from std
2. imports from external crates
3. imports from local modules
4. imports from self

This commit moves the colours module to be a sub-module of the output one.
This makes sense because finding which colour a certain file should be is only
done during output, and (I think) the only places that the `Colours` struct's
fields are ever queried is from the output module.

The only casualty was that the `file_colour` from the filetype module had to
be moved, as determining colours is no longer part of that module - only
determining filetype is. So it now reflects its name!

The benefit of this is that it make it possible to convert text cell contents
vectors into text cells with a method (see next commit). Casualties include
having to call `.into()` on vectors everywhere, which I'm not convinced is a
bad thing.

Because, strictly speaking, it's not a length, it's a width!

Also, re-order some struct constructors so that they're no longer
order-dependent (it's no longer the case that a value will be borrowed for one
field then consumed in another, meaning they have to be ordered in a certain
way to compile. Now the value is just worked out beforehand and the fields can
be specified in any order)

By removing the `File#file_name_width` method, we can make the file module
have no dependency on the output module -- in other words, the model (file)
and the view (output) are now separate again!

This commit introduces the `output::cell::DisplayWidth` struct, which
encapsulates the Unicode *display width* of a string in a struct that makes it
less easily confused with the *length* of a string.

The use of this type means that it's now harder to accidentally use a string's
length-in-bytes as its width. I've fixed at least one case in the code where
this was being done!

The only casualty is that it introduces a dependency on the output module from
the file module, which will be removed next commit.

A recent change to ansi-term [1] means that `ANSIString`s can now hold either
owned *or* borrowed data (Rust calls this the Cow type). This means that we
can delay formatting ANSIStrings into ANSI-control-code-formatted strings
until it's absolutely necessary. The process for doing this was:

1. Replace the `Cell` type with a `TextCell` type that holds a vector of
   `ANSIString` values instead of a formatted string. It still does the
   width tracking.

2. Rework the details module's `render` functions to emit values of this
   type.

3. Similarly, rework the functions that produce cells containing filenames
   to use a `File` value's `name` field, which is an owned `String` that
   can now be re-used.

4. Update the printing, formatting, and width-calculating code in the
   details and grid-details views to produce a table by adding vectors
   together instead of adding strings together, delaying the formatting as
   long as it can.

This results in fewer allocations (as fewer `String` values are produced), and
makes the API tidier (as fewer `String` values are being passed around without
having their contents specified).

This also paves the way to Windows support, or at least support for
non-ANSI terminals: by delaying the time until strings are formatted,
it'll now be easier to change *how* they are formatted.

Casualties include:

- Bump to ansi_term v0.7.1, which impls `PartialEq` and `Debug` on
  `ANSIString`.
- The grid_details and lines views now need to take a vector of files, rather
  than a borrowed slice, so the filename cells produced now own the filename
  strings that get taken from files.
- Fixed the signature of `File#link_target` to specify that the
  file produced refers to the same directory, rather than some phantom
  directory with the same lifetime as the file. (This was wrong from the
  start, but it broke nothing until now)

References:

[1]: ansi-term@f6a6579ba8174de1cae64d181ec04af32ba2a4f0

Fix compilation on arm using stable rust 1.5

Minor fixes for FreeBSD

src/feature/xattr.rs:6:5: 6:22 warning: unused import, #[warn(unused_imports)] on by default
src/feature/xattr.rs:6 use std::ffi::CString;
                           ^~~~~~~~~~~~~~~~~

$ exa --help
[...]
  -@, --extended     display extended attribute keys and sizes

$ exa -@
Unrecognized option: '@'.

$ exa --extended
Unrecognized option: 'extended'.

$ exa --git
Option --git is useless without option --long.

$ exa -l --git
.rw-r--r--  11k user 10 Dec 18:26 -- Cargo.lock
[...]

src/term.rs:37:39: 37:49 error: unresolved name `TIOCGWINSZ` [E0425]
src/term.rs:37     let result = ioctl(STDOUT_FILENO, TIOCGWINSZ, &mut window);
                                                     ^~~~~~~~~~

GitHub's new, wider view makes two screenshots side-to-side look nicer than one.

The buggy code assumed that, if output isn't to a terminal, then the only view available is the Lines view. This is incorrect, as the Details view doesn't require a set width either, so check for --long even when there's no set width.

This also includes some of the options that I forgot existed. Don't be mad.

The user can now control the output parameters by specifying the console width and when to show colours.

Fixes #75.

This puts the impls for the structs defined in the module first, then impls for the structs defined in the columns module second.

One of those two date formats was re-compiled before any date was displayed. Now they are compiled only the first time they're used, and cached versions are used thereafter, resulting in a speedup.

Instead of using the getopts crate’s dynamically-generated usage string, use a more static one:

- The options are organised by category now
- You can use `--help --long` to display only the ones that pertain to `--long`
- They’re aligned in a table sort of way

It could be generated statically, because all the options to change it are determined at compile time, but they’re not, yet...

Technically speaking, picking which timestamp to show for a file is a function of an output module, rather than the file itself. This also means that the `output::column` and `file` modules are now completely separate.

By taking the file names as a mutable vector, we can avoid having to allocate a new one when it’s empty. The recent changes to Options::getopts have made it more obvious that we could move the same vector out of getopts’s matches, instead of cloning it there.

We may as well use this trait now that it’s available!

With the new OptionSet trait, the from_word constructor doesn't really do much by itself.

This cleans up the options module, moving the structs that were *only* in use for the columns view out of it.

The new OptionSet trait is used to add the ‘deduce’ methods that used to be present on the values.

Move to stable