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 :)
For Family & Community Day? Not really sure. All I know is what's written at http://www.timeanddate.com/holidays/australia/family-and-community-day#obs, it seems to be uncertain (just predicted by this formula) for years beyond 2016.