v2.2.1 - Release

[Wenn0101]

Changelist:
-Fix problems with A1-A5 on Redboard form factor
-Fix error in SPI which resulted in the object not being deleted
-Reduce time of critical section in pwm_output (analog/servo out)
-Allow for RingBuffer.h to be included directly in projects/libraries
-Added functions interrupts() and noInterrupts()
-Update mbed core to clear serial errors
-update Example10 to show chip ID

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This discussion was created from the release v2.2.1 - Release.