* Introduce a trait for DMA channels
This trait is then used to hold types related to the particular DMA channel. This change allows us to simplify user-facing types.
* Remove private type from I2s
* Remove redundant spi3 example, update examples
* Merge markdown sections
* Add changelog entry
* Add the peripheral module plus some helper macros in preparation
* peripheral macro
* Add peripheral generation macro
* Fixes after rebase
* Update the signature of Peripherals::take
* syncronise hello world example
* fmt the entire repo
Co-authored-by: Jesse Braham <jesse@beta7.io>
