Lots of polishing, organizational changes, bug fixes, error handling etc. are
introduced.
COPY and NEW space thread creation are allowed but not thoroughly tested yet. It
seems they will work best if the lib supports utcb virtual range management
through the mapping.
Now, we support thread trees which are spanning more than one level depth. Any
thread can create any number of threads provided that they are under the limits
which are enforced by the kernel.
Also with this commit, we have almost finished supporting SHARED space thread
creation in which stack and utcb space are allocated statically.
