Support os x

[samth]

It would be great for this repo to show how to build on OS X on Travis. I think the needed steps are:

• Download the right dmg files for the various installers.
• Install them using the installer command.
• Figure out the right path to add to $PATH

[greghendershott]

Definitely a great idea.

Although I have access to OS X, I won't have time in the near future to do this.

[Danl2620]

I think installer only works with pkg files? Are those distributed anywhere?