Fixed --print and formatting
Removed pypy and added flake8 to travis configuration
Replaced argparse 1.2.1 with 1.1

Versions of argparse above 1.1 are not hosted on PyPi, and so will
not be installed by pip when using the default settings. Version
1.1 uses the Apache licence, whereas 1.2.1 uses the Python licence.

The tox configuration has been updated to use tox 1.6.0 or above,
which will install development packages using pip.