support for multiple client modules added. Refs: #156.
This allows, for example, that modules Coroutines and Co_Routines
can both be used. The Kernel's coroutine support ends when both modules are unloaded,
i.e. EndCoroutines has been called twice after initCoroutines has been called twice.

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