Add heuristic to remove parentheses

While parentheses in URLs are perfectly legal in positions even where
they don't make a lot of sense (like `https://github.com)`), they can
often lead to parsing errors when URLs are added in parentheses as side
comment (like `(https://github.com)`).

To improve the URL parsing when clicking on links, special heuristics
have been added which aim to remove parentheses in occasions where they
are not expected to be part of the URL.

This includes removing leading parentheses (like `((https://url.com`),
which are always removed before any other heuristic.

If the URL ends with closing parentheses, but there are no matching
opening parentheses in the URL (after stripping all leading
parentheses), the trailing parentheses will also be removed until there
are only matching parentheses left. This allows parsing URLs like
`https://github.com/de(mo).html)))`.

src/event.rs

@@ -135,6 +135,19 @@ impl<'a, N: Notify + 'a> input::ActionContext for ActionContext<'a, N> {
             buf.push(cell.c);
         }
 
+        // Heuristic to remove all leading '('
+        while buf.starts_with('(') {
+            buf.remove(0);
+        }
+
+        // Heuristic to remove all ')' from end of URLs without matching '('
+        let str_count = |text: &str, c: char| {
+            text.chars().filter(|tc| *tc == c).count()
+        };
+        while buf.ends_with(')') && str_count(&buf, '(') < str_count(&buf, ')') {
+            buf.pop();
+        }
+
         // Check if string is valid url
         match Url::parse(&buf) {
             Ok(_) => Some(buf),