GPIO optimization and tweaks

- Some functions marked inline
- Doc updated

src/uart.rs

@@ -1,4 +1,7 @@
-//! API for the UART peripheral
+//! # 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};
 use libm::floorf;