Changes:
<https://github.com/pygments/pygments/blob/f456d23496/CHANGES#L41-L253>
The most significant change is that lang='python' will now use the
Python 3 lexer by default. To get the Python 2 lexer, 'python2' must be used.
This seems like a sensible change, given the state of Python 3 adoption,
and the final version of Python 2 hitting EOL status last month. The
syntactic differences between Python 2 and 3 are minor.
Change-Id: I8a80a410b67035b97f03aacc6d8d71a97723fee8