Add reduce to Enum.Iterator protocol
Use reducers in Enum, File and URI

Remove Enum.equal?
Remove File.iterator/2 and File.biniterator/2
Remove iterator references in code
Remove file open in File.iterator and File.biniterator
Clean up and fixes in reducer code
Update docs for Enum.Iterator and reduce
Merge pull request #1102 from ericmj/reducers

Reducers