add simple render function

src/clj_jtwig/core.clj

@@ -1,6 +1,15 @@
-(ns clj-jtwig.core)
+(ns clj-jtwig.core
+  (:require [clojure.walk :refer [stringify-keys]])
+  (:import (com.lyncode.jtwig JtwigTemplate JtwigContext)))
 
-(defn foo
-  "I don't do a whole lot."
-  [x]
-  (println x "Hello, World!"))
+(defn render
+  "renders a template contained in the provided string, using the values in model-map
+   as the model for the template."
+  [s model-map & [{:keys [skip-model-map-stringify?] :as options}]]
+  (let [template (new JtwigTemplate s)
+        context  (new JtwigContext)]
+    (doseq [[k v] (if-not skip-model-map-stringify?
+                    (stringify-keys model-map)
+                    model-map)]
+      (.set context k v))
+    (.output template context)))