Support STM32F4Discovery with libmaple(wirish)

[kyab]

According to this thread(http://forums.leaflabs.com/topic.php?id=10456 ),Latest development effort for libmaple which support STM32F4 is going here.
https://github.com/AeroQuad/AeroQuad/tree/development/Libmaple.

On below link, @yamanekko Already succeeded to run mruby on STM32F4Discovery.
https://github.com/yamanekko/mruby-on-stm32f4discovery/wiki/build-mruby

[kyab]

I've succeeded with libmaple in AeroQuad. README.md should be updated.

[teachop]

@kyab I would be interested in the mruby+STM32F4 solution if you have time to update this project. Thanks.

[eugenio]

@kyab me too