Add CMakeLists.txt file specifically for tests.

  This compartamentalizes all options to building the tests, as well as
  information concerning them into a seperate module.

Add 'check' target to CMakeLists.txt build

  This option is only available if BUILD_TESTING is enabled, and acts
  much like the GNU Autotools 'check' target. It will build all tests
  and run them, instead of having to run make, then make test, and
  hoping the tests had been built during the first run.