Update README.rst

Added details about writing and running tests.
Update README.rst

Oh hey, ReStructured Text, not Markdown. :P
Merge pull request #3 from 0ion9/master

Python 3 support
Added tags to feature tests.
Fixed bug in dice expression compilation. Added tests for dice.
Another year, another release.

- Bumped to 0.6.
- Credited @0ion9 in new CONTRIBUTORS file.
- Added contribution guidelines
Added some ignores for project files.
Fix dice fix for python3.

Also improve clarity of division semantics;
a / b (where a is a results-list or a participant in an Operator) performs true division,
a // b performs truncating division (eg. 25 / 4 == 6).