Add update-with method to Map (#161)

Author: chrisrink10

basilisp/lang/map.py

@@ -149,6 +149,10 @@ def update(self, *maps) -> "Map":
         m: PMap = self._inner.update(*maps)
         return Map(m)
 
+    def update_with(self, merge_fn, *maps) -> "Map":
+        m: PMap = self._inner.update_with(merge_fn, *maps)
+        return Map(m)
+
     def _cons(self, *entries) -> "Map":
         try:
             e = self._inner.evolver()