Whitespace and comment cleanup
Added a TextInputMapper library class and subclass it in the example WordCountMapper
API change: context arguments to lambdas and
Simple{Mapper|Reducer|Combiner} classes no longer need parameter types.
These were redundant and unnecessary, since the
mapper/reducer/combiner classes themselves are parameterized.
Temporary directories between job stages now get deleted on job completion unless
-Dscamr.always.keep.interstage.files=true is set.
Prefer SnappyCodec -> LzoCodec -> DefaultCodec for intermediate and interstage compression