Specify can individual can pins from program

[phoenixs3]

While having default and alternate pin preset declarations is useful, for certain applications (such as mine) I use PB5 and PB13 for can 2. This is not possible without a library modification currently.

Ideally functionality would be: STM32_CAN Can2(CAN2, PB_5, PB_13);

[pazi88]

Didn't even know that you can mix the CAN TX and RX alternative pins like that. At least with F103 the RX and TX pins come in those predefined "pairs". Though for other ones that might be possible to do, but I haven't tested at all. If it works, I can add function for that.

[pazi88]

Closed via #45