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.
Added version and build status badges to README