fix: ability to change pll vcosel, disable pll outputs

feat: implement fmc sdram control

fix: unicode strings

feat: implement cdc application layer, fix enumeration

feat: implement enumeration fully

chore: update pin, exti, delay

docs: add documentation comments to most functions

feat: implement usb devicd cdc descriptors, init, setup

wip: usb

feat: rewrite main to use types

feat: add support for newlib

feat: toggle led on exti interrupt push button

feat: use cmsis for register definitions

Initial commit (template)