Channel: Fix bug in flatMapCh()
Resource: Improve interface
Aggregate: Implement headOption() and lastOption()
VarBuf: Implement map()
Buffer: Implement splitAt()
Map: Implement OptMap
Opt: Implement getOrElse() and orElse()
Map: Add test case for size()
VarBuf: Fix bug in map()

Newly added elements were not passed on.
Opt: Add toOption()
VarBuf: Implement forall()
Map: Implement forall()