contextmanager for stopping process only for given context
Merge pull request #26 from fizyk/stopped_context

contextmanager for stopping process only for given context
Update CHANGES.rst
extended docs about stopped context manager
Merge pull request #29 from fizyk/stopped_context

extended docs about stopped context manager
add failing test to illustrate terminate shell=True executors - refs #27
treat all processes as process groups - closes #27