Convert between international calling codes and countries and vice versa

This pull request is a new instant answer which implements yegg's [country-codes idea](https://duck.co/ideas/idea/17/country-codes).  

A user can type a query such as 'calling code +55' and get an instant answer which says, '+55 is the international calling code for Brazil'.  Users will also get useful responses for queries like 'calling code for Brazil'.  

I have tested this on Chrome and Firefox on Ubuntu.  

This probably needs a phone icon like [this](http://thenounproject.com/term/telephone/671/), but I haven't yet figured out where to put such an icon.  Hints?

![image](https://f.cloud.github.com/assets/104742/1897225/a1f17a22-7bd3-11e3-9b86-094ef1227bdd.png)