REPL namespaces; lib function for pattern matching

Adds support for REPL namespacing, primarily to avoid `main` collisions.
Also adds a library function for an ergonomic pattern matching function
that I've been noodling on. I might explore ways to make list syntax
less annoying specifically for pattern matching like this.

src/Parser.hs

@@ -255,9 +255,9 @@ parseSingleItemM = do
 
 parseVarM :: ParserM TricuAST
 parseVarM = do
-  token <- satisfyM (\case 
+  token <- satisfyM (\case
     LNamespace _ -> True
-    LIdentifier _ -> True 
+    LIdentifier _ -> True
     _ -> False)
   case token of
     LNamespace ns -> do