zframe updates and minor typo fixes

I really like your work to expose the CZMQ library to Python.
I was going to do this but you beat me to it - and I'm glad because its much better than I would have done.
Added zframe changes and a zframe test in line with czmq test.
Also added minor updates to types.py and fixed some typos.
The main motivation for these changes was to get access to non-string zframe.data buffer data. As well as sending standard string data I typically send serialised and compressed (binary) data in many of my ZMQ applications which gets corrupted with the assumption that zframe.data should always return a string.