Rewrite in Rust

Rererences:
- https://users.rust-lang.org/t/sysfs-vs-mmap-for-gpio-pwm-dma-control/23405/6 - Interesting comments on which DMA channel to use
- And https://github.com/besp9510/dma_pwm - Newer C lib for DMA access
- https://github.com/golemparts/rppal - Raspberry PI HAL - does not include PWM via DMA