Added support for "auto-formats".
Added and modified unit-tests.
`MockFileSystem` can use real files too, for when `vfsStream` doesn't work.
Use pretty colors for benchmark results.
Updated all external libs.

--HG--
rename : libs/lessphp/lessphp/LICENSE => libs/leafo/lessphp/LICENSE
rename : libs/lessphp/lessphp/lessify.inc.php => libs/leafo/lessphp/lessify.inc.php
Made the cache a bit more readable.
Added some more profiling to asset baking.
Changes to file processors:
- File processors get a logger and sandboxed access to the cache.
- The LESS processor is now using the 3rd-party cache-based compiler.
Don't force using the default plugins and themes sources.
Changes to plugins:
- The `plugin_info.yml` file is now required.
- The plugins' directory names are now less important -- name is taking from the
  plugin info file.
- Added `chef plugins update` command.
Added some pretty colors to the `plugins` and `themes` command.
The `chef` log can now handle console colors.
Fixed unit tests.
Updated CHANGELOG.
Fixed bug in `chef prepare post` where no extension was specified.
Fixed Windows-related path problems.
Cheaper regex-matching for the shallow FS.
Fix issues on Windows with cleaning after unit-tests.
Optimization to load pages less often from disk or cache.
This is done by not completely unloading a page when we can just invalidate the
rendered/formatted version.
More optimizations:
- Use object instead of arrays when possible.
- Try to reuse page objects a bit more.
(sadly this only improves performance by a few percents)