Fix PEP8 issues in gml.py
Rewrite GML parser and generator
Adjust GML test cases
Remove references to pyparsing
Avoid spurious empty lines due to str.split('\n') in GML parser
Simplify GML parser
Fix comments in GML parser and test cases
Make stringizer/destringizer in GML parser/generator raise ValueError
Make stringizer/destringizer in GML parser/generator raise ValueError (cont'd)
Fix docstrings of generate_gml and write_gml
Simplify GML parser and add list attribute handling
Comment about 'u' string prefix removal in GML parser
Enhance GML parser/generator tests
Enhance GML parser/generator tests (cont'd)
Fix GML parser compatibility with Python 3.2
Ensure that graph6 and sparse6 tests do no leave behind temporary files
add test for in-place replacement of self-loop node with node 0
bugfix: use ternary operator to replace node with self-loop in-place

because otherwise `old == target and new` with old equal to target will evaluate to new. If new is 0 (a valid integer node), then the conjunction evaluates to False, masking that old is equal to target. The ternary operator implements the selection and avoids this issue.
Merge pull request #1278 from johnyf/reinplace_selfloops

bugfix: reinplace self-loop node with 0 fails
Reimplement the network simplex method for min-cost flows