serial: trim COM from serial ports and add it when opening

[MatthieuDartiailh]

• [x] Closes #267
• [x] Executed black . && isort -c . && flake8 with no errors
• [x] Added an entry to the CHANGES file

[MatthieuDartiailh]

Will fail till https://github.com/pyvisa/pyvisa/pull/545 is merged

[MatthieuDartiailh]

Actually this revealed a more complicated issue. According to the VISA standard we only expect integers after the resource type (i.e. ASRL1::INSTR) and I started enforcing this in PyVISA, but it appears it will break serial on pyvisa-py both on Windows (but there we can easily fix it) and Linux where it is more complicated since the port can look like a path /dev/ttyAMA0.

I need to think a bit about how to fix this issue. The windows patch still makes sense to get a more homogeneous experience, but it won't be sufficient for Linux.

[MatthieuDartiailh]

I went with the option of allowing ResourceInfo board to be None which allows to preserve all previous and past functionality. This should be good to go.

[MatthieuDartiailh]

bors r+

[bors[bot]]

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