Added GPIO IRQ interface, refactoring

- 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

src/uart.rs

@@ -1,6 +1,7 @@
 //! # API for the UART peripheral
 //!
 //! ## Examples
+//!
 //! - [UART example](https://github.com/robamu-org/va108xx-hal-rs/blob/main/examples/uart.rs)
 use core::{convert::Infallible, ptr};
 use core::{marker::PhantomData, ops::Deref};