Add polymorph token

examples/push_struct.core

@@ -1,7 +1,7 @@
 MA :: #import "Arena.core"
 
 /*
-PushStruct :: (a: *MA.Arena, $Type): *Type
+PushStruct :: (a: *MA.Arena, $T: Type): *$T
 	size := size_of(Type)
 	result := PushSize(a, size)
 	return result

examples/unions.core

@@ -37,4 +37,4 @@ examples/unions.core - Error! Couldn't infer type of compound expression
 	c = {10}
 */
 
-	return 0
+	return 0