This patch introduces a super-simple format-diff tool, that allows you to do:
```
git diff | rustfmt-format-diff -p 1
```
To format your current changes.
For now it doesn't accept too much customisation, and it basically calls rustfmt
with the default configuration, but more customisation can be added in the
future if needed.
When there are no `[[bin]]` sections, all the binaries in `src/bin` are
automatically picked up. When a section is added, that is no longer the
case, so all the binaries need to be specified explicitly.
One notable feature is this this adds support for the experimental
`let x = loop { ... break $expr; }` syntax. This also includes a
test for formatting all the break and continue variations.
This will help in debugging issues as rustfmt gets more users.
If the working tree is clean, output looks like
$ target/debug/rustfmt -V
0.5.0 (9f5ed3b)
If the working tree is dirty, output looks like
$ target/debug/rustfmt -V
0.5.0 (9f5ed3b worktree dirty)
If git is unavailable, output looks like
$ target/debug/rustfmt -V
0.5.0 (git commit unavailable)
To avoid rebuilds on changing tests, the build script will only rerun if
files under src/ are changed. This means the actual git status may show
changed files and this would not show up in the version. This should not
be an issue as files not in src/ should not affect the build output.
On unix, `term::stdout()` just reads the `TERM` environment variable to
decide what features are available. It does not check if the output file
descriptor is in fact a tty. This resulted in printing escape codes when
redirecting output.
