This allows the DAC to use a user-specified Timer for the triggering
(instead of the default Timer(6)), while still supporting original
behaviour.
Addresses issues #1129 and #1388.
Blanket wide to all .c and .h files. Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.
Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.
Simple but functional timer control. More sophistication will
eventually be added, or for now just use direct register access :)
Also added pyb.freq() function to get MCU clock frequencies.
Reads ADC values into a bytearray (or similar) at a fixed rate. Needs a
better name and improved API. Also fix up DAC dma function (which also
needs a better name and API).
