Shared emulator library and extern "C"

Runtime/stm32/make/app.mk
Runtime/stm32/make/emulator.mk 
The emulator shared dynamic library can be made with changes to the files. But, the libemulator.so is also building and copied in other folders e.g. .../tests other then .../build folder.

Runtime/stm32/cores/wiring_digital.h
Runtime/stm32/cores/wiring_digital_pinmode.h
The extern "C" wrapper is added to the functions written in C++ in above files, so that the functions can be called from ctypes module in Python.