A simple 'blinking LED' program for the STM32F3 Discovery board which the 'Embedded Rust' ebook targets.

It looks like the ebook is a work-in-progress, since the code samples stop a bit after the 'Hello World' section. But that's okay; what's there is well-written and it provides enough information to get started with the core peripherals.

This project uses the 'cortex-m-quickstart' template and the stm32f30x_hal crate

There are two compiler warnings about deprecated GPIO pin methods. I'm not sure whether I'm calling it wrong or the HAL crate is out of date, but suggestions are welcome.