feat: Initial stemmer feature

test/lancaster_stemmer_test.gleam

@@ -0,0 +1,13 @@
+import gleeunit
+
+pub fn main() -> Nil {
+  gleeunit.main()
+}
+
+// gleeunit test functions end in `_test`
+pub fn hello_world_test() {
+  let name = "Joe"
+  let greeting = "Hello, " <> name <> "!"
+
+  assert greeting == "Hello, Joe!"
+}