This pulls all common functionality into `shared-bindings` and keeps
platform-specific code inside `nrf`. Additionally, this performs most
validation in the `shared-bindings` site.
The only validation that occurs inside platform-specific `common-hal`
code is related to timeout limits that are platform-specific.
Additionally, all documentation is now inside the `shared-bindings`
directory.
Signed-off-by: Sean Cross <sean@xobs.io>
