Add file/directory handle parameters to FuseOperation

[matil019]

Resolves #11

This PR adds a file handle parameter and directory handle parameters to FuseOperation. This is a API-breaking change.

Summary

• Added parameter fh to fuseSynchronizeFile
• Added type variable dh to FuseOperations
• Added return value dh to fuseOpenDirectory
• Added parameter dh to fuseReadDirectory, fuseReleaseDirectory and fuseSynchronizeDirectory

dh would correspond to DirStream, which is a Haskell representation of DIR *.

[plredmond]

I've integrated this branch into my project and it works great. There doesn't seem to be a function in the posix package which can be used to implement fuseDirectorySyncronise, however, but that's not important for this PR.