Add read and write impl for Serial, Irq flags functions and RTIC example

[brain113]

Hi,
This pull request adds Read and Write implementations to Serial and few functions to work with Irq flags.
This needed to add more control under communicaiton flow and timing.

Also I added an example how to use this with RTIC. The example uses DIR pin when transmiting (like RS485).

PS: This is my first pull request ever :)

[Sh3Rm4n]

PS: This is my first pull request ever :)

Whoooho. Pretty exciting stuff. I'm happy to be the reviewer of your first PR 🎉

This PR looks pretty good. One minor nit, and you also have to make rustfmt happy via cargo fmt --all and clippy has also some minor thing to say: https://github.com/stm32-rs/stm32f3xx-hal/runs/2765167229

Thanks for your PR. I'm pretty excited about this as well, as this comes with the first RTIC example for this project! 😄

[Sh3Rm4n]

Even though these are the correct types hinted by the compiler, there exists type aliases, which are easier to read. I'd recommend them:

Suggested change

	type SerialType = Serial<stm32f3xx_hal::pac::USART1, (gpio::Pin<gpio::Gpioa, U<9_u8>, Alternate<PushPull, 7_u8>>, gpio::Pin<gpio::Gpioa, U<10_u8>, Alternate<PushPull, 7_u8>>)>;
	type DirType = stm32f3xx_hal::gpio::Pin<gpio::Gpioe, U<13_u8>, Output<PushPull>>;
	type SerialType = Serial<stm32f3xx_hal::pac::USART1, (gpio::gpioa::PA9<A7<PushPull>>, gpio::gpioa::PA10<A7<PushPull>>)>;
	type DirType = stm32f3xx_hal::gpio::gpioe::PE13<Output<PushPull>>;

[brain113]

Hi,
thank you for the warm welcome!
I added additional commit to make rustfmt and clippy happy.

Actually I don't understand why clippy make me to change
init::LateResources {serial, dir}
to
init::LateResources {dir, serial}
the struct definition is
struct Resources { serial: SerialType, dir: DirType, }
so the "serial" field is the first.

[Sh3Rm4n]

This is pretty strange indeed. A wild guess: Maybe it has something to do with the rtic #[resources] proc-macro, which reorders the fields under the hood and this makes clippy complain?
I don't know. Would be worth looking into, but it does not really matter right now.

Thank you really much for your contribution. Nice PR! 👍