fix access calls

for some reason, linux version of fuse does not call access functions,
but OSX version does. This should fix them and enable mounting on OSX.
raise EROFS in ReadOnlyView access

access() should raise EACCES on but ReadOnlyView always raises EROFS. In
general the ReadOnlyView behabior should move towards rising EACCES,
since not the entire filesystem in in read only mode.
Merge pull request #138 from calind/osx

fix access calls
Fix #140 (Chmod on folder throws error)
Fix #139 (Return error on invalid chmod).
Merge pull request #141 from PressLabs/fix-chmod-on-dirs

Fix chmod (restrict modes to 0755, 0644 on files and 0755 on folders).
Update README.md
added simple demo
Merge branch 'master' of github.com:PressLabs/git-fs
Update README.md
some memory optimizations