Add maps; remove map emulation functionality from list; function and tags now internally use maps instead of lists

test/tests/map assignement.ans

@@ -0,0 +1,20 @@
+:x = {1,2}
+
+{x}
+
+{x(1) := 3}
+
+{x}
+
+{x("foo") := "a"}
+
+{x}
+
+{x("bar") := "b"}
+
+{x}
+
+{x("foo") := "c"}
+
+{x}
+