Add short-cut to !.

src/engine.rs

@@ -52,6 +52,9 @@ pub const FN_ANONYMOUS: &str = "anon$";
 /// function to compare two [`Dynamic`] values.
 pub const OP_EQUALS: &str = Token::EqualsTo.literal_syntax();
 
+/// Standard not operator.
+pub const OP_NOT: &str = Token::Bang.literal_syntax();
+
 /// Standard concatenation operator.
 ///
 /// Used primarily to build up interpolated strings.