introduce TableContext
introduce TableContext:next
introduce TableContext:next
introduce TableContext:next row
introduce TableContext:move columns left right
introduce TableContext:delete column
introduce TableContext:insert column
introduce TableContext:kill row
introduce TableContext:insert row
introduce TableContext:move row up down
introduce TableContext:insert hline
introduce TableContext:insert hline and move
introduce TableContext:split column down
introduce TableContext:join lines
introduce TableContext:remove unused methods