Addresses #1048.
Node labels must be within double quotes. Addresses #1048.

Tuple labels are now converted to strings:
   (1,2) -->  "(1,2)"
Add omitted quote=True option to escape(). #1048.
Add unit test for #1048.
GML read/write with numeric HTML entities. #1061
Merge pull request #1048 from chebee7i/gmlbug

Better .gml handling. Fixes #1048. Fixes #1061.