Use file(GENERATE) to create a CTestConfig file

[bruxisma]

Calling include(CTest) breaks a lot of stuff in what would be an otherwise normal build situation. One particular issue is that by calling enable_testing(), we can no longer make a custom target named test that also builds the unit test executables. In some places this build-and-run-tests target is called check, however we would like cmake --build check to be designated for clang-check. As such, we need to override all the CTest related machinery, including generating a CTestConfig file. We can do this via file(GENERATE), much like we would like to in #6. One additional feature we get out of this is the ability to
ignore ctest altogether. This will let us do things like hook into other project's unit test runners, or submit additional information to a code coverage service, such as codecov.

[bruxisma]

Closing, as this project has burned me out, and I cannot continue working on it in its current state. CMake has changed massively since this project was started. Most of it is no longer necessary. A new repository will be launched in September.