Trailing commas

Author: Sainan

docs/QoL Improvements/Trailing Commas.md

@@ -0,0 +1,15 @@
+Parameter and argument lists are allowed to have trailing commas in Pluto.
+
+```pluto
+local function print_favs(
+    color: string,
+    food: string,
+)
+    print($"My favorite color is {color}, and my favorite food is {food}!")
+end
+
+print_favs(
+    "red",
+    "pizza",
+) --> My favorite color is red, and my favorite food is pizza!
+```