add F103xB platform

[kd0aij]

adds support for 16 bit system timer defaults 16 bit system timer to 10KHz and 32 bit timer to 1MHz adds type micros_time_t with 32 or 64 bit resolution for timing.c::micros() changes timer function scheduling to use micros_time_t instead of systime_t reduces timing_state_update_task_func interval from 10 seconds to 5 seconds since systime_t wraps every 6.5536 seconds at 10KHz

NOTE: MICROS_TIME_RESOLUTION of 64 bits is untested, but is only needed if there is a requirement to specify intervals > 1 hour with microsecond resolution

TODO:

• [ ] clean up GPIOv1 initialization: palSetPadMode doesn't seem to work for alternate output functions

[jschall]

I'd like to accept this. We're still working on how the OMD framework is licensed, though. The more copyright holders there are, the more difficult it will be to change it from GPLv3. Would you be willing to sign some kind of CLA?

[kd0aij]

@jschall What kind of license are you considering? My only concern with a more permissive license is that I might never see bugfixes or enhancements contributed back to things I've worked on. But I don't know that the GPL provides any assurance of that either.