client.shared: Convert API documentation markup to the Sphinx format.

Translate API documentation markup, included in docstrings, to the
format that Sphinx documentation engine accepts.

The changes are very simple but massive, the following markups
were translated:

* @param to :param
* @type to :type
* @attr to :attr

Signed-off-by: Ruda Moura <rmoura@redhat.com>