Drop support for Python 3.3.
Install coverage package.

* Ignore coverage byproduct.
Drop utest script. Report test coverage.
Enable coveralls support.

* Install a coverage badge.
* Invoke coveralls.io after a successful build.
Mention flake8 instead of pep8.
Merge pull request #72 from Renelvon/coveralls

[WIP] Install coveralls and cleanup build.
AST, Parse, Parse test: Separate constants from functions.

* Add ConstantDef node.
* Parse parametre-less function definitions as constants
* Require param_list to be non-empty (i.e. param_seq)
* Adapt parsing unit tests accordingly.