* add isFileName
* add hasParentDir
* add hiddenFile
* add our own openFd version for more control
* small documentation improvements
* add a getDirectoryContents' version that works on Fd
* fix linting warnings
* lift version constraints in benchmark
Also adjust HPath.IO to work with the new API.
'canonicalizePath' was missing, making this function far less reliable.
In order for this to work we have to work around circular imports
with a IO.hs-boot file.