adding Coroutines to BlackBox. Refs. #156.
Coroutines for BlackBox based on Windows fibers as originally inspired by the CPC package 'CO_' by Dmitry V.Dagaev.
The API is reduced to a single module more in the tradition of Modula-2 coroutines.
Kernel services such as garbage collection and trap cleaners/checkers are integrated.

Signed-off-by: Josef Templ <josef.templ@gmail.com>