Use Travis CI to build/upload runnable jars to s3
Misc travis-ci build tweaks

* Add faraday_middleware gem to address travis-artifacts error:
    /home/travis/.rvm/gems/ruby-1.9.3-p484/gems/faraday-0.9.0.rc7/lib/faraday.rb:189:in `lookup_middleware': :json is not registered on Faraday::Response (Faraday::Error)
* Move gem install to after_success so builds that fail, fail faster
* Make PROJECT_VERSION available to all build stages
Pin to faraday version 0.8.9

To address: https://github.com/travis-ci/travis-artifacts/issues/23
Farady 0.8.9 is the latest version known to work with travis-artifacts.
Add shasum and adjust upload paths
TRAVIS_BRANCH may have spaces

(Also test that artifact uploads with the same version will overwrite
each other.)
Build a tgz artifact modeled on past releases
Use a hyphen instead of underscore
Use a hyphen instead of underscore
Merge pull request #177 from mesosphere/artifact_publishing

Automatically upload marathon build artifact (tgz) to s3 with shasum