EG: move compose to same level as observabe

    in preparation for C version of observable.all
EG: rename extension to "ext"
EG: _obsevable.c compiles into same extension

    not being used yet.
EG: use is_generator to cope with AllGenerators
EG: creating AllGenerator works
EG: added AllMessage to extension + unit tests
EG: using is_generator() all over
EG: observeble + compose in c working
EG: I think it works; all tests do.
EG: done
EG: enabled a few more tests for c