implement iseq, tests

Signed-off-by: Ava Hahn <ava@aidanis.online>

src/lex.rs

@@ -212,7 +212,7 @@ fn process(document: &String) -> Result<Box<Seg>, String> {
  */
 fn tok_is_symbol(token: &str) -> Option<String> {
     for t in token.chars() {
-        if !t.is_alphanumeric() && t != '-' && t != '_' {
+        if !t.is_alphanumeric() && t != '-' && t != '_' && t != '?' {
             return None;
         }
     }