Add circleci 2.0 support

[springmeyer]

This adds support to mapbox-tile-copy for running test on circle ci. Their are several motivations for this PR:

• Travis has been flaky recently, not only due to some flapping tests (Tests are horribly blippy #77) but also several types of travis failures to launch.
• I wanted to learn circleci
• I've heard circleci is faster

This tests mapbox-tile-copy 3 ways:

• On OSX
• On ubuntu
• Inside docker, also running ubuntu

Compared to travis:

• Builds start instantly
• Jobs run in 3-3.5 minutes, which is about a 1 minute faster than avg travis jobs

/cc @kkaefer for review
/cc @GretaCB for visibility

[springmeyer]

How appropriate, this PR is failing on travis with:

Err:22 http://ppa.launchpad.net/chris-lea/redis-server/ubuntu trusty/main amd64 Packages
  Unable to connect to ppa.launchpad.net:http

Going to merge and run them together for a bit, then plan to disable travis soon.