A presentation layer for qtree with tests.
Adding qtree method to expressions, in order to hook them into the new output layer.  Start adding tests for the qtree methods.  Next up, automatically compiling a LaTeX document which might help us make sense of our test failures.
Good progress - got the And renderer working for single complex lhs and rhs, but tricky now dealing with double complex lhs and rhs.
WIP - checkpoint
Hooray - working - still a test failure, but it's a test bug.
Merge pull request #3 from lukemarsden/master

Working prop tree renderer