Multi-dimensional COLUMN handling

[mcdittmar]

Need to check the response for a column whose value has multiplicity > 1 (ie: an array).
See test_reader.py::test_parsing_columns()

• MultiObj.b is an array element of type ivoa:real[2]
  o for CONSTANT and LITERAL, this results in 'list of float', [ r1, r2 ]
  o for COLUMN, this results in 'list of length 1 of MaskedColumn'

• MultiObj.a (scalar)
  o LITERAL - float n/a v1
  o CONSTANT - float n/a v1
  o COLUMN - MaskedColumn(float) shape(2,) [r1v1, r2v1]

• MultiObj.b (array)
  o LITERAL - list(float) len=2 [v1, v2]
  o CONSTANT - list(float) len=2 [v1, v2]
  o COLUMN - list(MaskedColumn(float)) len=1 <<< This doesn't look right
  list[0] = MaskedColumn shape(2,2) [[r1v1, r1v2],[r2v1, r2v2]]

• Handled by: framework.VodmlDescriptor::select_return_value()
  o this is the base class for Attribute, Reference, Composition
  o current logic looks OK for Reference and Composition, but not Attribute
  o probably want override in Attribute
  Composition max = -1 for unbound (so if not making override, take into account)

rama/rama/reader/votable/tests/test_reader.py

Lines 136 to 147 in c1fc61a

	def test_parsing_columns( columns_file ):
	"""
	Test parsing of COLUMN elements
	<COLUMN dmtype ref >
	<OPTIONMAPPING>
	<OPTION>"string"</OPTION>
	<ENUMLITERAL>"vodml-id"</ENUMLITERAL> or <SEMANTICCONCEPT>
	</OPTIONMAPPING>
	</COLUMN>
	The parser pushes the Table rows into value arrays