Expand unit test suite to guard against regression

This release is primarily devoted to beefing up the unit test suite - expanding coverage of existing tests and adding a new test. The expanded tests now check the sequence of lifecycle event notifications published for each corresponding test method.

In the process, I noticed and fixed a few instances where I'd specified JUnit assertion imports for TestNG test classes. I fixed these.

I also expanded the README content to include links to the implementations of supported test runners.