Add pinout for package information to STM32 devices

[salkinium]

Replacement for #40.

The type is implicitly "i/o", and thus only added if it's not.
The mapping from name to <gpio> must be done in user software, the code for this is rather simple:

def pin_name(name):
    name = name[:4]
    if len(name) > 3 and not name[3].isdigit():
        name = name[:3]
    return (name[1:2].lower(), name[2:].lower())

cc @tgree