initial state may be sequential states

this place was missed when introducing enhancement #29.
when resuming workflow machine execution after it was suspended, the
start state is validated against the state machine's logical
constraints for this case.
instead of guarding against non-event states (which now are allowed) we
only guard against final states.
resolves #30
removed left over argument, meh #30
added tests to increase code coverage

found and fixed two bugs along the way (invalid exception syntax o0)
resolves #32
updated chglog and composer deps
fixed changelog wordings
using internal fireEvent insteadof emit
added missing unset to AbtractParser.tearDown