ENH: DelimitedTextReader supports string input.

Enable vtkDelimitedTextReader to take a text string as
the input.

Change-Id: I3d9b8dd0db9dfcd5afd9a6f4bbdc06accd942d94
Merge topic 'DelimitedTextReaderAcceptStringInput' into master

ade77513 ENH: DelimitedTextReader supports string input.