Implement part of connection parsing

Implement part of connection parsing

This is a broken commit. I came this far before I realized it will be
better to store buses as vectors of ids in the name_to_id (formerly
io_to_id) dictionary. That will make accessing the dictionary and
iteration over the pins of buses much easier.
name_to_id dict will therefore hold union of t_id and t_vec<t_id> for
pins and buses respectively.