This removes openssl and makes the binary properly self-contained.

The last PR was meant to remove the duplicate bitflags, but I think I messed it up and another one crept in.

* Also remove bitflags as it isn't used.
* Don't update ansi_term as ANSIString is no longer Clone.

See #97 and recently #130 too.

This allows the user to pass in options such as "--ignore '*.pyc'" to not list any files ending in '.pyc' in the output. It uses the Rust glob crate and currently does a simple split on pipe, without any escaping, so it’s not really *complete*, but is at least something.

Thinking about it, it doesn't make sense to use an *external* time zone source when the program we want to compare it to, ls, uses the system one. So just use the system one.

Also, handle the case where the time zone data file can't be loaded by showing the files in UTC rather than falling over and quitting.

- Fix visibility errors I stupidly didn't test before committing earlier
  today
- Silence warnings about casting that were necessary for ARM
- Update dependencies

Travis didn't like the old versions.

- Users v0.5.1, which renames OSUsers to UsersCache
- Locale v0.2, which returns to libc v0.1
- Datetime v0.4.2, which mimics the locale update, and puts timezone definitions in:
- Zoneinfo-data, which is needed to obtain the current timezone

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

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.

Changes to the way ANSIStrings work mean we need to dereference the strings before putting them in an ANSIString. There's more that can be done here, but this gets it to compile for now.

This should prove more stable than relying on a Git version.

- VariableOffset -> TimeZone::VariableOffset

This commit removes the threadpool in `main.rs` that stats each command-line argument separately, and replaces it with a *scoped* threadpool in `options/details.rs` that builds the table in parallel! Running this on my machine halves the execution time when tree-ing my entire home directory (which isn't exactly a common occurrence, but it's the only way to give exa a large running time)

The statting will be added back in parallel at a later stage. This was facilitated by the previous changes to recursion that made it easier to deal with.

There's a lot of large sweeping architectural changes. Here's a smattering of them:

- In `main.rs`, the files are now passed around as vectors of files rather than array slices of files. This is because `File`s aren't `Clone`, and the `Vec` is necessary to give away ownership of the files at the appropriate point.
- In the details view, files are now sorted *all* the time, rather than obeying the command-line order. As they're run in parallel, they have no guaranteed order anyway, so we *have* to sort them again. (I'm not sure if this should be the intended behaviour or not!) This means that the `Details` struct has to have the filter *all* the time, not only while recursing, so it's been moved out of the `recurse` field.
- We use `scoped_threadpool` over `threadpool`, a recent addition. It's only safely used on Nightly, which we're using anyway, so that's OK!
- Removed a bunch of out-of-date comments.

This also fixes #77, mainly by accident :)

The separator_width field in the term_grid crate was replaced with a filling field.

Fixes #39!