This also matches the documentation order from the
filepath package more.

* 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.

Breaking the callstack with an ioError seems a bit harsh here.

'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.

This also removes 'canonicalizePath' from HPath which fixes
the doctest.