Previous one didn't refresh by last use. Use the stdlib version for py3
and one of our own for py2.
Max size set to 512, which should be fine for everyone (tweaking is
still possible by monkeypatching, as the tests do, but I don't want to
make an interface of it).
Make all library code compatible with both Python 2 and Python 3. Helps
move to modern Python idioms. Can now write for Python 3 (with
workarounds for Python 2) instead of the other way around.
In the future, when it is eventually time to drop Python 2, the library
will be in a better position to remove workarounds
Added a very small comparability module compat.py where required. It
includes definitions for:
- text_type -- A type. str on Python 3. unicode on Python 2.
- string_types -- A tuple. Contains only str on Python 3. Contains str &
unicode on Python 2.
