Added mbed-events from https://github.com/ARMMbed/mbed-events. Changes
from upstream:
- the whole code is licensed under the Apache license. Sources and
headers were updates with this information.
- removed the porting layers for Windows and FreeRTOS and the references
to these porting layers in equeue_platform.h.
- moved the TESTS directory in mbed-events to the TESTS directory of
mbed-os.
Bogdan Marinescu