* Reset SWD lines to SWD rather than GPIO. This makes OpenOCD happier.
* Default speaker enable lines to False for CircuitPlayground to prevent
the speaker from buzzing when no sound is playing. Fixes#126
Also replace use of PINMUX_DEFAULT with PINMUX_UNUSED to prevent any
accidental pin changes. This caused user SPI to break internal SPI
flash on the Feather M0 Express.
Fixes#100
Scott Shawcroft