First STM32F051 version that compiles.

This version is able to compile Arduino Sketches,
but they don't actially do anything yet.  Maybe the
system gets initialised right, maybe not, that hasn't
been tested yet.

At preparing this, there was some confusion how to
actually create the right Makefiles.  To prepare this,
do the following:

  pushd hardware/arduino/sam/variants/ellduino_stm32f051/build_gcc
  make

That will create the required library binary.