EUSTM32F103RC - First cut of support for this High-Density STM32F103
series development board.

These boards can be picked up for less than $11, coupled with a 10DOF
sensor board they make a great development platform or cheap expandable
FC.

Pretty much all pins are available to be used, unlike on the less
capable and more expensive OLIMEXINO.
Alternate layout for a 31-LED quad. Disabled by default.