Massive cleanup

First, sorry about the patch dump and it's messy state. This was basically implemented by looking at the docs, finding something a bit inconsistent or strange, fixing it, etc. The main goal here was making hidtools a python module in its own right so it can be easily used by other script instead of being a supporting module by the hid-recorder tools.

This is also on top of !14 (merged)

Main interesting changes in this patch set:

• almost full sphinx documentation
• new submodule hidtools.hut which contains the HUT as lookup for usages and pages/names from the data files. This is what parse_hut was before, but moved around and improved.
  • the HUT isn't a dict subclass anymore, this is generally not recommended in python anyway, too many side-effects. It's now dict-like instead.
• hiding a few more things from the unsuspecting user
• promoting the hidraw report descriptor into a ReportDescriptor object

One of the remaining things that I have on the list are changing HidField.usage and HidField.usage_page to return the respective HidUsage and HidUsagePage objects so we can convert in the callers where needed.