Merge pull request #13 from vasily-kirichenko/master

FileSystem TP invalidates itself if any child dirs/files changed in any way
FileSystem type provider invalidates itself whenever any child dirs/files changed in any way
Better docs for the FileSystem type provider.
Remove "watchForChanges" since it's broken
Better FileSystemProvider tests
Remove unused helpers - closes #14
Allow to use nCrunch
Fixing path releated bugs in FileSystemProvider
FileSystem TP calls Invalidate() not more than once per second