embedded-dma-hal

This crate is a (very brief) encapulation of DMA-related traits suitable for use in a HAL. It is extracted from and based upon Jorge Aparicio's dma work in his stmf32f103xx-hal crate. I include this crate as a dependency of my work on the STM32L4x6-hal crate, and intend to use it in device drivers as a complement to embedded-hal.