Produce CSV string from Csv object

* Add a separate Csv.toCsvString to produce a CSV with all the contents of the Csv object (regardless of the length)
* Slightly change Csv.toString so it only shows "..." when there more lines that aren't being displayed
Unit test Csv.defineOutputColumns
Construct Csv from List[List[String]]

to facilitate parsing the CSV outside of Planet7
Update README.md
Merge branch 'stuff' of https://github.com/jcaraballo/planet7

Add the ability to pimp external CSV parsers as relational data sources, so that we can use their more advanced parsing upstream of transforming our CSVs.
Merge branch 'stuff' of https://github.com/jcaraballo/planet7

Add the ability to pimp external CSV parsers as relational data sources, so that we can use their more advanced parsing upstream of transforming our CSVs.
Update README.md
Make String a RelationalDataSource
Make operation names clearer and introduce map() for operating over Csv rows
Rename some specs
Add Csv.filter(), starting with an AND filter
Version we are about to release