Add support for optional debug parameters
Update debug documentation for clarity and accuracy
Add printFields and printTuple interval support
Update to use builder pattern for options
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	scalding-core/src/main/scala/com/twitter/scalding/RichPipe.scala
Update to take function instead of object
fix reference to pipe
Add a Stats object that can be used to increment and access counters.
Remove parens.
Changed logic to only take counter name but assume a fixed group.
Also print custom counters after job completes, based on a command line arg.
Rename custom counter group.
Dump custom counters by default.
Allow counters to use groups.
Simplify Grouped/CoGrouped/CoGroupable types
Fix for regression introduced in last commit
Encode the grouping rules in the types
Avi's observation that HashJoinable <: CoGroupable
minor cleanup of KeyedPipe
Move HashJoinable to its own file