- 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
- Clock module to set and retrieve system clock which can have
varying frequencies. Also allows enabling peripheral clocks
- Prelude updated
- Common time types added, based on stm32f1xx HAL implementation
- Basic timer implementation added
