Maple Bootloader with modifications to run on the LeafLabs Audio Board, 
which runs off of an stm32f103RET6 instead of an RBT6. The changes between
the regular bootloader and this one are:

config.h - 
    added a FLASH_PAGE_SIZE parameter, which is used in flash_erase_pages
    moved the LED/BUT pins to their proper places

usb.h
    changed wMaxTransferSize to FLASH_PAGE_SIZE
    moved the DISC pin to its proper place

hardware.c
    flash_erase_pages now depends on FLASH_PAGE_SIZE


FILES -------------------------------------------------------------------------

stm32lib/*
  - all the (possibly consolidated) stm32 lib and usb example code

usb.c 
  - USB-specific hardware setup. Interrupts, clocks, etc. handling USB when 
    not "Attached". some low-level callbacks (low power mode, init, reset, 
    resume, etc).

usb_callbacks.c 
  - aka endpoints: handling data transfer when "Configured". calls out to 
    application specific callbacks (eg DFU or serial shit)

usb_descriptor.c 
  - aka application descriptor; big static struct and callbacks for sending
    the descriptor. 

main.c
  - main loop and calling any hardware init stuff. timing hacks for EEPROM 
    writes not to block usb interrupts. logic to handle 2 second timeout then
    jump to user code. 

hardware.c
  - init routines to setup clocks, interrupts, also destructor functions.
    does not include USB stuff. EEPROM read/write functions.

dfu.c
  - mostly the giant FSM case switch, also some USB endpoint callbacks


TODO --------------------------------------------------------------------------

 * use sizeof() for usb application descriptor