Bring the runtime tests up to date and start running them

[brson]

The tests in src/rt/test are compiled but never run. It's almost certain that they are completely broken. Right now all they are accomplishing is making it difficult to change parts of the runtime.

Replace it with a standard C++ unit testing framework and start running the tests.

[brson]

I think the thing to do here is just scrap the rt test framework and the existing broken tests, plug in a new one, add it to the build system and write a few example tests to get people started.

[brson]

The old runtime tests have been deleted. I spent half a day looking into C++ test frameworks, but got bored and frustrated.

[brson]

This is becoming less important as we are writing very little C++ code these days.