This is a bootloader derived from leaflabs' maple dfu bootloader.
It has a better support for multiple boards, and some other
goodies.
To compile run 'make'
To specify toolchain - use CROSS_COMPILE, e.g.
'CROSS_COMPILE=arm-none-eabi- make'
Results are piled to build/ directory.
To see what's actually happening - run with V=y, e.g.
CROSS_COMPILE=arm-none-eabi- make V=y
This will dump a lot of info for you.
Have fun.

WHY?
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I needed a bootloader for my custom boards. Upstream maple was
shitty in places. So I cleaned up the mess

WHAT'S THE DIFFERENCE, COMPARED TO MAPLE's UPSTREAM ONE?
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Easy to add new boards
Configurable FLASH_PAGE_SIZE per-board
Configurable bootloader enter and leave conditions. per-board.
Configurable descriptors. per-board.
Extra options to save space
Batch-compile for all boards.
Pretty colored compilation output.
Configurable altsettings, easy to add new download targets
Multiple downloads in one run support.4
New altsetting: download-to-run
Compiles with -Os, and works when compiled like that
a LOT faster:
   Max USB download speed - 61 Kilobytes/s.
   Real Life flash programming speed - 20 Kilobytes/s