Added support for compilerFlags in source list. If any source file
metadata (like compilerFlags) is attached to a directory the metadata
propagates downwards to all children recursively until the files are
reached.
Files are now processed in the same way as directories in `getSources`
this depends on #108 to not over-eagerly cache groups. The `source` is
propagated as metadata down all the way (thanks @yonaskolb)
Fixtures and unit tests are updated as well.
Brandon Kase
Yonas Kolb