Enhances the display of the list of virtualenvs
Compatibility with python 2.7, Pypy and Pypy3
Compatibility with python 2.6 and improvements for tox and travis conf
Make travis build in parallel for each python version
Refactored print_utils
disable sudo on travisCI
Fix tests on pypy3
Use the backported get_terminal_size in the main pew command as well
Fix spurious expected failures
Make `pew in venv` start a subshell

Currently `pew in myvenv` is an invalid command. It makes sense for
it to run a sensible default command in the virtual env, and a
sensible default command would be a subshell. This proxies that
currently invalid command to be the same as `pew workon myvenv`.