add compile_to_lua helper function

spec/etlua_spec.moon

@@ -112,6 +112,18 @@ This is my message to <%= [=[oh yeah  %>"]=] %>]]
       out = fn {}, buff
       assert.same "firsthelloyeah", out
 
+    it "should compile readme example", ->
+      parser = Parser!
+
+      first_fn = parser\load parser\compile_to_lua "Hello "
+      second_fn = parser\load parser\compile_to_lua "World"
+
+      buffer = {}
+      parser\run first_fn, nil, buffer
+      parser\run second_fn, nil, buffer
+
+      assert.same "Hello World", table.concat buffer
+
   describe "Parser.in_string", ->
     cases = {
       { "hello world", false }