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)