Feature(KATE): hilight (url) links.
Refactor(MD): refactor the main program to prepare for future automatic testing.
Feature(MD): Implement better querying (allow attribute querying).
Feature(DEFS): Work on proof (styling + Proof of ... types).
Feature(DEFS): End nested proofs with a full square (instead of the empty one).
Misc: Whitespace changes.
Misc(HTML): Update MathJaX configuration.

  -- MathJaX version 2.3 supports automatic linebreaking
  -- scale math down to 80% to fit in with surrounding text
Misc(TODO): Add/Reorganize TODO items.
BugFix(HTML): Add a space after the title.
Misc(MD): Move the logger out of main.
Doc(MD): Add method documentation.