ResourceWarnings in test suite with Python >=3.2

When warnings are enabled (e.g. using PYTHONWARNINGS="d" environmental variable or -Wd option), then some ResourceWarnings occur when running tests with Python >=3.2.

./test_markdown2.py:207: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/sublist-para.tags' mode='r' encoding='UTF-8'>
  for line in open(tags_path):
./test_markdown2.py:187: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/pyshell.opts' mode='r' encoding='UTF-8'>
  opts = eval(open(opts_path, 'r').read())
./test_markdown2.py:187: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/link_patterns_edge_cases.opts' mode='r' encoding='UTF-8'>
  opts = eval(open(opts_path, 'r').read())
./test_markdown2.py:207: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/link_patterns_edge_cases.tags' mode='r' encoding='UTF-8'>
  for line in open(tags_path):
./test_markdown2.py:187: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/html_classes.opts' mode='r' encoding='UTF-8'>
  opts = eval(open(opts_path, 'r').read())
./test_markdown2.py:207: ResourceWarning: unclosed file <_io.TextIOWrapper name='./tm-cases/html_classes.tags' mode='r' encoding='UTF-8'>
  for line in open(tags_path):
...

Start in test_markdown2.py at lines 187 and 207, where the reported unclosed files are opened while running the test suite. Run the tests with PYTHONWARNINGS="d" or -Wd enabled and inspect those paths. Done means the test suite no longer emits the listed ResourceWarnings.