Remove unused TransposedFrame.
Correct documentation of fromColumns/fromRows.
Map now replaces the col/row, rather than append.
Add usecase documentation for fromColumn and fromRows.
Rename some Frame constructors.

This renames fromGeneric -> fromRows, adds fromColumns, and renames the
old fromeRows and fromColumns to mergeRows and mergeColumns.
Add documentation for reduce, and Rows version.
Add reduceByKey to Frame.
Remove confusing function addColumn.
Add more docs.
Rename map{Row,Col}Index to map{Row,Col}Keys.
Rename Series ++ to orElse, add actual ++.
Simplify "genericJoin" in Frame.
More docs and simplifications.
Remove trait sketch that was abandoned.
Remove unnecessary language imports.

The higherKinds feature was just added as a flag to scalac instead.
Rename mapCell to cellMap.
Fix documentation error.
Fix bug in Series#getAll.
Make ordered/unordered Index constructors private.