Enable testing from root directory

[mohd-akram]

As per the documentation:

Note that ctest expects to find a test file in the build directory root. Therefore, this command should be in the source directory root.

enable_testing() in the Release subdirectory has no effect when cmake is called with the root file causing a make: *** No rule to make target `test' error when running make test.

[BillyONeal]

Thanks for your contribution!