[core] Move command regexp generation to tools.
[core] Add automatic generation of tests from @example decorators.

-Add new module test_tools.
-Change the structure of callables example attribute to be a list of dicts.
-Move generation of command-regexps to tools.
[calc, rand, units] Convert examples to tests.
Add pytest script and config files.
Merge branch 'master' into example_tests

Conflicts:
	willie/tools.py
Merge pull request #297 from embolalia/example_tests

Add generation of unit tests from examples