events: WIT_EVENT_DEFINE

new macro for defining events. So we don't need to do it manually (but
we can). Also it checks for the legality of opcode and interface.
Old function wit_event_define was removed
events: check if opcode is ok in eventarray_add

check if opcode is in range specified by interface
events: add WIT_EVENTARRAY_DEFINE() macro

creates eventarray and initializes it.
tests: added basic tests for event and eventarray

The will be more later