* Add boot2 feature. Add boot2 linkage into each BSP optional on feature
* Enable boot2 feature in BSPs by default. Remove boot2 decl from all BSP examples
* Add EXTERN in memory.x for BOOT2_FIRMWARE, rename bootloader static slice to BOOT2_FIRMWARE
* Update new examples and itsy_bitsy BSP to use boot2 feature
* Remove boot2 as a dev-dependency for the BSPs, no longer needed
* Add no_mangle BOOT2_FIRMWARE to adafruit_macropad
* Fix itsy-bitsy blinky - it wasn't using the BSP, so it didn't get BOOT2_FIRMWARE linked in
* Created an itsy bitsy rp2040 board support package adapted from the bsp of the qt py rp2040. Special thanks to ithinuel for help in matrix
* Changed the board description so it doesn't match the qt py rp2040
* Changed blinky.rs to itsy_bitsy_blinky.rs and ran changes through cargo fmt
