extract: add arbitrary port width matching

[phsauter]

The goal is to improve extract and make it easier to use in scenarios similar to the ones described in the extract example.

The final goal is to extract something like a multiplier followed by an arbitrary amount of variable-width adders.

ToDo:

• [ ] minimum port widths per port (in user port matching)
• [ ] avoid expanding ports to max width with 'Z
• [ ] document in macc examples