Release 1.0.0-alpha.10

*** This is (also) an alpha release with breaking changes (sorry) ***

Added

• Added pwm::SetDutyCycle trait.

Changed

• gpio: add ErrorKind enum for consistency with other traits and for future extensibility. No kinds are defined for now.
• delay: make infallible.
• i2c: remove _iter() methods.
• i2c: add default implementations for all methods based on transaction().
• i2c: document guidelines for shared bus usage.
• spi: SpiDevice transaction now takes an operation slice instead of a closure.