Before this change, `microcontroller.cpu.uid` returned values
where the top 4 bits of each byte were zero, because of
an incorrect bitmask used in this function.
shared_bindings/index.rst: updated Support Matrix format as discussed in PR #503 & Issue #448.
shared-bindings/microcontroller/Processor.c & .h: added UID lookup functionality for use with all ports. Fixes#462.
* Added asf4_conf/samd*/hpl_sercom_config.h
* Adjusted clocks in peripheral_clk_config.h.
* Put some frozen libs back in CPX for testing.
* Implement common-hal I2C
* Add samd*_peripherals.h in parallel with samd*_pins.h for common
functions and data.
* Store SERCOM index in pins table for convenience.
* Canonicalize some #include guard names in various .h files.
simpler reset of SERCOMs; remove unused routine
