Add class wrappers for module data retrieval

Wiliam Souza complained about ugliness in API, so we'll try to make it
a bit more acceptable by using objects for module data access. This way
we can e.g. get a subinstrument by calling a method in the instrument
object instead of exposing C structures.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>