fixed parameter union and added more checks

descriptions were not merged before. Added checks to avoid incompatible
data and tests
nicer parsing of strings with angled brackets

and better error messages
fixed bug in parameter union
added spec for 2d tables
tests for 2d table
implementation for 2D tables
removed sort field again

sorting is not a property of the table, but of the Table Index. One gets
into trouble when using more than one table.
store choices for table indices in Parameter class

and figure out their sorting. Also test cases for that
check column lengths on tables while parsing