Refactor a bit the code
Separate arguments and parameters by a space

Separate arguments and parameters by a space instead of an equals
sign, as both short and GNU long options can be specified this
way.
Fix a bug: search for the right value

We need to look up for the option, not the option's value in
the optional_params list.
Protect regexes by start and end anchor
Improve example.py and its associated spec