Fixed map-columns.
Minor fixes.

- fixed slices
- added type check
- made map-rows accept a single key
Added DFRAME as a nickname.
Renames select*-rows to mask*-rows.
Updated unit tests (for new function names).
Added COUNT-ROWS (with unit tests).
Added do-rows.
Renamed AO: to AOPS:.
TRANPOSE was moved to CLNU.
Fixed bug (renamed function was left in code).