Added head & tail to Coproduct
Rename Coproduct append/Append to extendRight/ExtendRight
Added extendLeft to Coproduct
Adding scanRight to HLists
Adding scanLeft and scanRight to tuples. Documentation.
Merge pull request #163 from wheaties/scanLeft

Scan left
Merge pull request #166 from stacycurl/coproduct-head-n-tail

Added head & tail to Coproduct
Merge pull request #168 from stacycurl/extend

Renamed Coproduct.append to extendRight, added extendLeft