Use primitive modify function in Point instead of primitive set.
Slight code cleanup of abstract lens code.
Lenses are now constructed by providing a modifier.

Not a setter.
Implemented TH deriving code for the new labels.
Merge branch 'primitive-modify' into arrow-fail

Conflicts:
	src/Data/Label/Abstract.hs
	src/Data/Label/Derive.hs
	src/Data/Label/Maybe.hs
Renamed Failure to Failing.
Fixed Either labels after merge of 'primitive-modify'.
WIP