Fixes #44, crash when no handlers

Recent database handler changes made the library crash, when feed
object is created without channel, item handlers (passing nils).
These simple changes seem to fix the problem and the library works
again.
Merge pull request #45 from Paulius-Maruska/bug/crash-without-handlers

Fixes #44, crash when no handlers
Ensured that New() feed function is functionally equivalent still
Typo in comment
Merge pull request #46 from JalfResi/split-handlers

Separating singular handler type to ease reuse/chaining