Add doctest module & TestCase, TestSuite & DocTestOutput classes

Refs #9874
Parses documents where all tests passed.

Refs #9874
Add unit test for all passed case and fixed problems unit test found.

Refs #9874
Parser and tests for all pass and all failure cases.

Refs #9874
Finish parsing of mixed pass/fail document.

Refs #9874
Write out xunit XML when Sphinx build has finished.

This only happens if the builder type is set to doctest.
Refs #9874
Add a test for multi-document output.

Refs #9874
Change xunit output file to match those produced by ctest

Refs #9874
Add in some debug statements.

Refs #9874
Activate the mantiddoc.doctest extension

Refs #9874
Use lxml for xml if it is available.

Refs #9874
Add package information to XML doctest output.

Refs #9874
Fix classname for tests part of fail suite.

Refs #9874
Fix unittest after classname change.

Refs #9874
Fix parser when encountering testcleanup/testsetup failures.

Refs #9874
Raise exception doctest build-finished handler if there was an error.

Refs #9874
Fix regex for finding failed test name.

Refs #9874
Merge remote-tracking branch 'origin/feature/9874_doctest_xunit_output'