Initial Release

First working copy of nrf bootloader that works with Arduino framework.
Advertising name set to SENDANCE_DFU.

Hex file contains bootloader + softdevice.

To download to uC:

nrfjprog -f nrf52 --reset --program debug_feather-express_bootloader-d5b9d97_s140.hex --sectoranduicrerase

Debug version is used for now.