Add Gleam implementation (#548)

* Add Gleam implementation

gleam/test/gilded_rose_test.gleam

@@ -0,0 +1,8 @@
+import gilded_rose.{Item, update_quality}
+import gleeunit/should
+
+pub fn update_quality_test() {
+  let inventory = [Item("foo", 0, 0)]
+  let assert [new_item] = update_quality(inventory)
+  new_item.name |> should.equal("fixme")
+}

gleam/test/program_test.gleam

@@ -0,0 +1,5 @@
+import gleeunit
+
+pub fn main() {
+  gleeunit.main()
+}