Tutorial 0-4 implemented for typed tutorial.
most of Tutorial5 (joins) implemented
working on getting Tutorial5 to do the right thing
working Tutorial 5
refactor comments
clean up comment
add comments, put 'TextLine()' into each case
move out of the 'typed/' directory
fix tabs -> spaces
incorporate style feedback

- avoid qualified names (add imports)
- use camelCase, TypedPipe.from, parentheses for simple closures
- use TypedTsv for word scores (and add 'word_scores.tsv') to
  demonstrate using typed sources
- also improved comments a bit
get rid of explicit CoGrouped/UnsortedGrouped references, explain types in comments
Refactor TextLine and add 'OffsetTextSource' which keeps the offset field

For simplicity, TextLine in the typed DSL discards the byte offset which Cascading provides. This source is an alternative that keeps around the offset.
rename OffsetTextSource -> OffsetLineSource
use OffsetLineSource in typed tutorial
move OffsetLineSource up next to TextLine
rename OffsetLineSource -> OffsetTextLine
remove commented-out lines
explicit TypedPipe.from, add section on interop
remove duplicate default
start adding flag