Added new documentation, new devices (WIP) and units.
Merge branch 'dev' of github.com:cgranade/gpibusb-comm_code into dev
Continued work on SRS 345 refactoring.
Fixed import errors. Still broken on Win w/o VISA.
Added catch for WindowsError when importing PyVISA.

This is now done in a way as to not break on other OSs, where
Python doesn't define WindowsError.
Fixed misc bugs causing problems with the SRS345.
Fixed URI handling of gpib+usb scheme.
Merge pull request #7 from Galvant/dev

Pull from upstream
Merge pull request #9 from cgranade/dev

Bug fixes, SRS 345 refactoring