Support for Adafruit Bluefruit Feather 32u4 (and related) + ps2->ble converter

[ramonpoca]

Also useful for those working with UART-based Adafruit Bluefruit modules.

@tmk Even though you might consider not merging this due to the inclusion of many Adafruit/Arduino files, I leave the PR as a reference for somebody who might want to apply it to their tree.

[tmk]

@ramonpoca, completely agree with you, this would be really useful for people who want Bluefruit LE support.

Also they may be interested in this: it seems qmk_firmware has suppport for Bluefruit LE with SPI. https://github.com/qmk/qmk_firmware/blob/9de443cbf10ac41bc15762c9c83f138f51dd3b9a/tmk_core/protocol/lufa/adafruit_ble.cpp