Add makefile for tests

[muraliadithya]

With the solver changing several times, it is useful to have a test suite that runs on various simple and complex tests, as well as edge cases that we may encounter using the solver in various places.

The idea is to have a single command like 'make tests' that executes the tests using appropriate options for each one and displays results of how many succeeded or failed. This will likely involve writing some kind of comment-like structured text at the top of each such test file that specifies what options to provide.