Release 1.0.0-alpha.7

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

Added

• Error traits for CAN, SPI, I2C and Serial are implemented for Infallible.

Fixed

• Fixed blanket impl of DelayUs not covering the delay_ms method.

Changed

• spi: traits now enforce all impls on the same struct (eg Transfer and Write) have the same Error type.
• digital: traits now enforce all impls on the same struct have the same Error type.
• serial: traits now enforce all impls on the same struct have the same Error type.
• i2c: traits now enforce all impls on the same struct have the same Error type.
• i2c: unify all traits into a single I2c trait.

Removed

• Traits with unconstrained associated types and their modules (See: #324, #354):
  • capture::Capture
  • pwm::Pwm
  • pwm::PwmPin
  • qei::Qei
  • timer::Cancel
  • timer::CountDown
  • timer::Periodic
  • watchdog::Disable
  • watchdog::Enable
  • watchdog::Watchdog