Added STM32F411RE to list
Added "M4F"

Several listed as Cortex M4 cores are actually M4F cores (having a floating point unit), I did some homework to figure out which ones have FPU's. It appears that the K20D50M is the only board with a Cortex-M4 MCU that is does not have a floating point unit.
Merge pull request #415 from 23chrischen/patch-2

Added STM32F411RE to list