Enumerate exercises and add 'Solution' headings

hamming_distance.lua

@@ -1,17 +0,0 @@
-function hamming_distance(str1, str2)
-   -- Your solution here
-end
-
--- Tests -----------------------------------------------------------------------
-
-local luaunit = require("luaunit.luauint")
-
-function test_distance_between_foo_and_bar_is_3()
-   luaunit.assertEquals(hamming_distance("foo", "bar"), 3)
-end
-
-function test_distance_between_bar_and_baz_is_1()
-   luaunit.assertEquals(hamming_distance("bar", "baz"), 1)
-end
-
-os.exit(luaunit.LuaUnit.run())