Handle delete key in cmdline

[bynect]

If there is a character after the cursor delete that, otherwise delete the current character.

If the deletion should only delete the character after the cursor these change must be made:

    fn cmdline_handle_delete(&mut self) {
        if self.cmdline.cursor_forward().is_some() {
            self.cmdline.delc();
        }

        if self.cmdline.is_empty() {
            self.cmdline_hide();
        }
    }