Added improved functionality for the 'conversion-rule' tag.
It works for primitive, container and value types. Object types doesn't have conversion rules because they can not have implicit conversions, and the regular conversion is always the same (get C++ object held on Python wrapper, and finding/creating a Python wrapper to a C++ pointer).
Unit tests were added. Documentation was updated.
Reviewed by Luciano Wolf <luciano.wolf@openbossa.org> Reviewed by Renato Araújo <renato.filho@openbossa.org>