Don't memoize evaluated process in append, fby, onFailure, onComplete

Memoization may cause space leak.
Merge pull request #6 from radekm/space-leak-fix

Don't memoize evaluated process in append, fby, onFailure, onComplete
Fix continuous signal so it always returns newest value
Merge pull request #7 from radekm/fix-signal-continuous

Fix continuous signal so it always returns newest value