* added example for Feather RP2040
For the HAL, currently just passes the feature to the PAC. Also pass the 'rt' feature through to the HAL for all the BSP crates.
Bring in line with atsamd-hal GPIO v2 Copied as much as possible. Docs lifted mostly as-is. Also add sample BSP for the Feather RP2040 in boards/feather_rp2040 May include a few random fixes from currently futile attempt to get doctests working.