Initial I2C HAL implementation.
Only the I2cMaster was tested so far, I2cSlave will be tested next.
Master side was tested with a temerature sensor example application
in the vorago-reb1 crate
- Adds the IRQ interface to configure interrupts on output and input pins
- Moved the `FilterClkSel` struct to the `clock` module, reexporting in `gpio`
- Added function to set clock divisor registers
- Clearing output state at initialization of Output pins
- Added utility function to set up millisecond timer
