Fixes #54 using the datetime crate's spiffy new time zone ability.

Colours are now disabled when output is not to a terminal. Fixes #53!

This required some internal restructuring - colours are now in their own object that gets passed around everywhere it's needed.

Exa now uses the new IO, Path, and Filesystem libraries that have been out for a while now.

Unfortunately, the new libraries don't *entirely* cover the range of the old libraries just yet: in particular, to become more cross-platform, the data in `UnstableFileStat` isn't available in the Unix `MetadataExt` yet. Much of this is contained in rust-lang/rfcs#1044 (which is due to be implemented in rust-lang/rust#14711), but it's not *entirely* there yet.

As such, this commits a serious loss of functionality: no symlink viewing, no hard links or blocks, or users or groups. Also, some of the code could now be optimised. I just wanted to commit this to sort out most of the 'teething problems' of having a different path system in advance.

Here's an example problem that took ages to fix for you, just because you read this far: when I first got exa to compile, it worked mostly fine, except calling `exa` by itself didn't list the current directory. I traced where the command-line options were being generated, to where files and directories were sorted, to where the threads were spawned... and the problem turned out to be that it was using the full path as the file name, rather than just the last component, and these paths happened to begin with `.`, so it thought they were dotfiles.

Still missing a few Beta features, but it compiles!

- Copy requires Clone
- current_dir returns a Path now
- num_cpus moved to a crate

- Changes to users crate

- old_path::Path isn't imported by default anymore
- range -> ..

This stops the openssl-sys version clash preventing exa from compiling.

This compiles, but with manymany warnings.

- Update package versions
- locale::default -> locale::english
- Argument handling changes

This has been mostly done with changes in the datetime crate's suddenly
supporting locales.

It's still important that the user's locale is touched only once and
cached from that point on, so a struct in output::details has been made
public, along with that module. This will change later as that object
gains more and more uses thoughout the codes.

Use the `locale` crate as a dependency to read in the set
thousands-separator character, and pass this to the file size column,
which uses it to add the separators in.

en_GB uses ","
fr_FR uses "" and just displays the numbers in one go.

This prevents crates.io from doing weird things from a circular depedency, which is probably my fault.

Using the datetime crate, add an extra column to the --long view that
prints out the modified, accessed, or created timestamp for each file.
Also, let the user pick which one they want to see based on the --time
command-line option.