Autotest API documentation (initial effort)

Hello, this change sets represents my  (with big help of @clebergnu)  initial effort to create the API documentation for the Autotest by means of using sphinx-apidoc and all docstring presented in this project. The documentation API (the output) is hosted at http://autotest.readthedocs.org.

For compatibility with sphinx (the standard engine that Python uses for documentation), the docstrings tags that uses at "@" (like @param  and @return) are replaced by colon ":" (like :param and :return), all new docstring documentation must follow this new convention.