allow HumanDocReadingError to raise, closes #6

echod only takes one argument, I should stop copy-pasting from
vim-ipython, though maybe @mattjj and @chrisjordansquire  didn't watch
the 20 minute demo over at http://bipython.org/pages/demo.html

I covered the `ipython console` step 10 minutes in.
give informative error on old ipython

though there should be a way of getting it to work - but now that 2.0 is
out, everyone should be using that... conflicted.
make bipython python3 compatible

thanks to python-modernize for doing the lifting here.

In particular, I used @bfroehle's fix_add_future branch from
https://github.com/mitsuhiko/python-modernize/pull/5
3 at last, 3 at last! Thank Guido almighty, we're python 3 at last!

closes #7
fixed typo, thanks @stefanv for catching!
added link to the screencast
formatting README.md
bipython2/bipython3 and report Python on --version
sync version reporting and releasing
fix version reporting
fix keyword completion in python3

seems like kwonly isn't being used here at all anymore, should look into
that later.
fix docstring display on repeated tab
rudimentary local history
added version printing