Add a new target for AddressSanitizer as extra credit

One of the things we do in the C track is have a separate compilation target for validating memory accesses, which we do using AddressSanitizer. We should implement a similar check here by adding a new target into each exercise's CMakeLists to run the tests under ASan, and document that to describe it as extra credit for the students in the 'Running the Tests' doc page.

Possibly add a build with MemorySanitizer as well to track uninitialized reads, but ASan is generally more useful.