Add Frame appendRows and appendCols methods.
Extract classifiers into Classifiers trait
Add tests for filterByValues and filterByKeys
Add test coverage for foreach* methods
Add test coverage for filterEntries and cellMapWithKeys
Add test coverage for some reduce methods
Add test coverage for Series.max and min
Add test coverage for sum and product
Merge pull request #40 from pellucidanalytics/topic/frame-append

Add Frame appendRows and appendCols methods.
Bump version to 0.2.1.
Add ColumnBuilders.
Merge pull request #42 from mrvisser/hackday-Aug29-2014

Test coverage improvements
Bump version to 0.2.2.
Switch dep order so framian dependsOn framianColumn.
Add memoize method to Column.

This method will ensure that values are memoized in the return column.
For empty columns or dense columns, this does nothing. But for evaluated
columns (columns that wrap a function Int => Cell[A]), it will ensure
their evaluation function is evaluated at-most-once (though perhaps
optimistically).
Merge branch 'master' into topic/column-sanity