2.0 beta

Changelog:

• Variable type standardization to ease porting
• New Timing structure to ease porting, see Timing.h
• Arduino Zero compatibility (c59fa8f) by @EsbenSoeltoft
• pullDownFast cross-architecture function by @EsbenSoeltoft

Bugfix:

• can_start bugfix now reading 10 bits (6ceb2cb)
• read_byte bugfix (d2679d5)
• Infinite collision bugfix (#43)