Provide a compile-time snake_case solution via typesystems

After the introduction of the:

from __feature__ import snake_case

which enables a snake_case for all the camelCase Qt methods, it's normal to think of having such feature for people using their own binding with Shiboken.

For this, we could add an option per module or per function to create an alias of the function, so both are available when generating the python module.