Re-export all peripherals to the module

[Sh3Rm4n]

So that this is not needed:

use stm32f3xx_hal as hal;

use hal::spi:Spi;
use hal::pac::SPI1; // <-- this seems un-intuitve for first time users

This is better I think:

use hal::spi::{Spi, SPI1};

or

use hal::spi::{Spi, periph::SPI1};