Fix #45: support escaping of ')' and ':' in kirby tags with backslash

E.g.:

(link: http://github.com/ text: (#\))

(link: http://github.com/ text: some (text\) in (\) title: The Title)

(link: http://github.com/ text: some (text\) in (\) and title\: in text title: The Title)