Implement EVs (events?)

[DCNick3]

Those are started with EVBEGIN and ended with EVEND commands

They do not allow fast-forwarding

They can be skipped as a whole (jump to EVEND) by pressing B

Questions:

• I haven't seen any messageboxes there. Is it possible to have one? How do they behave?
• Can stuff like interruptible wait (WAIT with first arg being 1) be interrupted? How do SELECTs work? Are events fully non-interactive?