config+url: add support for user-defined regex patterns

Users can now define their own regex patterns, and use them via key
bindings:

    [regex:foo]
    regex=foo(bar)?
    launch=path-to-script-or-application {match}

    [key-bindings]
    regex-launch=[foo] Control+Shift+q
    regex-copy=[foo] Control+Mod1+Shift+q

That is, add a section called 'regex:', followed by an
identifier. Define a regex and a launcher command line.

Add a key-binding, regex-launch and/or regex-copy (similar to
show-urls-launch and show-urls-copy), and connect them to the regex
with the "[regex-name]" syntax (similar to how the pipe-* bindings
work).

input.c

@@ -349,9 +349,9 @@ execute_binding(struct seat *seat, struct terminal *term,
             action == BIND_ACTION_SHOW_URLS_LAUNCH ? URL_ACTION_LAUNCH :
             URL_ACTION_PERSISTENT;
 
-        urls_collect(term, url_action, &term->urls);
+        urls_collect(term, url_action, &term->conf->url.preg, true, &term->urls);
         urls_assign_key_combos(term->conf, &term->urls);
-        urls_render(term);
+        urls_render(term, &term->conf->url.launch);
         return true;
     }
 
@@ -448,6 +448,42 @@ execute_binding(struct seat *seat, struct terminal *term,
         term_shutdown(term);
         return true;
 
+    case BIND_ACTION_REGEX_LAUNCH:
+    case BIND_ACTION_REGEX_COPY:
+        if (binding->aux->type != BINDING_AUX_REGEX)
+            return true;
+
+        tll_foreach(term->conf->custom_regexes, it) {
+            const struct custom_regex *regex = &it->item;
+
+            if (streq(regex->name, binding->aux->regex_name)) {
+                xassert(!urls_mode_is_active(term));
+
+                enum url_action url_action = action == BIND_ACTION_REGEX_LAUNCH
+                    ? URL_ACTION_LAUNCH : URL_ACTION_COPY;
+
+                if (regex->regex == NULL) {
+                    LOG_ERR("regex:%s has no regex defined", regex->name);
+                    return true;
+                }
+                if (url_action == URL_ACTION_LAUNCH && regex->launch.argv.args == NULL) {
+                    LOG_ERR("regex:%s has no launch command defined", regex->name);
+                    return true;
+                }
+
+                urls_collect(term, url_action, &regex->preg, false, &term->urls);
+                urls_assign_key_combos(term->conf, &term->urls);
+                urls_render(term, &regex->launch);
+                return true;
+            }
+        }
+
+        LOG_ERR(
+            "no regex section named '%s' defined in the configuration",
+            binding->aux->regex_name);
+
+        return true;
+
     case BIND_ACTION_SELECT_BEGIN:
         selection_start(
             term, seat->mouse.col, seat->mouse.row, SELECTION_CHAR_WISE, false);