update outdated dev examples to transys api changes

type checking is better enforced now, so several check=False alternatives don't exist any more. Adding states and transitions and labeling them happens by calling the same methods and is more explicit now, so more readable (though a bit more verbose, but using keyword-arguments is much friendlier).
rename X0reach to mem

because it is more descriptive of that variable's role
bugfix: FSA.atomic_propositions shouldn't point to the alphabet
improve exception message for LabeledDiGraph untyped edge attributes
bugfix: states.initial not callable any more
bugfix: states.select_current has been deleted
doc fix: LabeledDiGraph.add_edge