picoC for TauLabs

This is the result of the discussion at #998. It implements the picoC interpreter into Taulaubs. Users can write little functions for their own hardware without branching the complete source. Sadly, this is a F4 only party. Becase picoC uses too much RAM, which smaller targets don't have. But the performance is really impressive.
On the picoC usart source files can up- and downloaded. There are no gcs routines yet. But the mechanics to do this via gcs is already built in.