Add G20 day (Brisbane) and show day (Cairns)

See http://www.justice.qld.gov.au/fair-and-safe-work/industrial-relations/public-holidays/dates for G20, and http://www.justice.qld.gov.au/fair-and-safe-work/industrial-relations/public-holidays/2014-show-holidays for Cairns.

I'm working on a data mining project at the moment, to add all the regional Australian holidays. Expect more pull requests soon :)
I'm not crazy about having a function just to have it available in 2014 but...we don't have another way to do this at the moment. So I'm happy with it as it stands.