Add tests, fix BoundedRational bugs

Add back some basic test infrastructure from the KitKat calculator,
updated to make it work with the current code base and asynchronous
expression evaluation.

Add BoundedRational tests, designed to check that we get all the
corner cases, particularly for degree-based trig functions, right.

Fix a couple of BoundedRational typos that caused these tests to fail.

Change-Id: I81d8f3d9bde6aa6c20f9958eabd62979babeff5b