Adds a bunch of unit tests, removes old file from test directory

I added a bunch of unit tests to `test/gol_clojure/core_test.clj` so now we can be more confident our code works, and we have built in test cases :smiley: They're not perfect (nor do they test every case), but they're better than nothing!

I also think they reveal a few code smells; for instance, the `new-row` function returns a vector of a different length than the rows of its input matrix.