The bootloaders are in [1], [2] and [3].

The firmware, which gets loaded by the bootloader, has to make an USB reset for 
reenumeration. For this compile the firmware with "make Bootloader=1".

Once the bootloader is flashed, you flash the new firmware like this:
First run /path/FlashDFUxxx.sh /path/newFirmware.bin,
then (re)connect or reset or reboot the board.

I made a patch for dfu-util, which lets's dfu-util loop, so this needs no longer be done in a script.
dfu-util git contains that patch [4].

[1] https://github.com/j1rie/maple-bootloader/tree/unify_platforms
[2] https://github.com/j1rie/STM32F103-bootloader
[3] https://github.com/j1rie/STM32F105-bootloader
[4] git://git.code.sf.net/p/dfu-util/dfu-util