Add GD32F10x to known datasheets

[dmlambo]

Hello @maxgerhardt ! I've made some changes to add support for f103, but with only moderate success.

• added the datasheet quirks
• added more "A" family distinguishing features, such as for PeripheralPins.c

I hope this doesn't go against the grain for you, it's a new codebase for me. :) If you want to grab the relavent parts and merge it yourself, by all means!

What's not in the change, obviously, are all the additions to ArduinoCore-GD32 to make it compile. There wasn't too much to be done to get it going, just adding the startup files, variants, and the GD32F10x_firmware (cmsis/spl).

I got to a point where it was compiling and I could upload firmware, but I don't have an external debugger, so I can't say where it stops, other than it stops in the bootloader. I tried changing the FLASH offset with no luck. I'm not going to look into it any further without a way of actually debugging it.