Custom lexers can now terminate operators

New constraint: custom lexer output is dropped whenever it is used to terminate an operator nested inside another custom lexer, because the recursive call has to return exactly one lexeme

orchid-api/src/lexer.rs

@@ -28,7 +28,7 @@ impl Request for LexExpr {
 #[derive(Clone, Debug, Coding)]
 pub struct LexedExpr {
 	pub pos: u32,
-	pub expr: TokenTree,
+	pub expr: Vec<TokenTree>,
 }
 
 #[derive(Clone, Debug, Coding, Hierarchy)]