fix doNext and added doCompleted
Add 'take' operator
restore the original semantics to doEvent
Merge remote-tracking branch 'upstream/master' into do-next-completed

Conflicts:
	Signal/Operators.hs
	Tests.hs
Merge branch 'master' into do-next-completed

Conflicts:
	Signal/Operators.hs
	Tests.hs
Remove need for an argument in the doCompleted lambda
Merge branch 'do-next-completed'