Previous pins definition stated that the UART1 RTS and CTS were not connected. They are connected and can currently be used via A1 and PWM0 respectively. To make things a little clearer, enabling the RTS1/CTS1.
To me, it made more sense to track which boards go together in a cluster;
when reviewing a request to actually use a duplicate vid/pid, you want
to know what board(s) it is aliasing.
I also revamped the detection of non-USB boards so that a board .mk file
that couldn't be parsed by the code here would raise a problem instead
of just being skipped for the purposes of checking.
There were some lines with comments on the end, and some variation in
capitalization of the IDs. These are all normalized and a (sometimes
unfriendly!) error printed when it's incorrect.
Before this, here were some ways to trick the duplicate vid/pid checker:
```
USB_PID = 0XABCD
USB_PID = 0xAbCd
USB_PID = 0xABCD # harmless comment?
```
None of these things were ever done on purpose.
