Add NSData constructor from a git_buf
Add -[GTBlob applyFiltersForPath:error:]
Add NSData.git_buf accessor
Use NSData <> git_buf conversion in GTFilterList
Invalidate the buffer given to git_dataWithBuffer:
Tests for NSData+Git
The True Meaning of nil for +git_dataWithBuffer:
Fix extraneous space
Use UTF8String for paths possibly libgit2-provided

The filesystem representation is always precomposed, which may be
undesirable.
Merge pull request #376 from libgit2/filtered-blob

Add -[GTBlob applyFiltersForPath:error:]