Cleanup testdata

Closes #18

* Add testPathFromName()

  Finds the name of the test in the TESTDATA_FILES global.

* Add testPathsFromDirectory()

  Finds all tests in testdata and add the paths to the TESTDATA_FILES global.

* Finish standardizing tests into formal structure.

  Tests with "xx.xx" as were parsed out of other test files from docutils but
  not yet ready for implementation. For example, when splitting out the section
  tests into test data, some tests included definition list features that are
  not yet implemented. The tests were added to the definition list test
  directory but given the "xx.xx" numbering.

* Change "_" to "-" in test names.