urgent fixes in test harness

@rismoney

A couple months ago, minitest released a major new version that broke compatibility and caused tests to fail on ruby 1.9 for anybody who ran `bundle install` *after* the new minitest was released.

This pull request fixes compatibility within the test harness, adds testing on ruby 2.0, adds new unit tests, and provides cleanup. This pull request does *not* affect functionality of the package provider.

Specific commits include:

* README: render markdown on Github web gui
* spec_helper: improve exception handler
* spec_helper: avoid traceback with minitest 5
* spec_helper: avoid NameError exception on Minitest 5
* Gemfile: require Minitest 5
* Gemfile: Add travis and travis-lint
* spec: add unit tests to validate .travis.yml
* travis: add current puppet versions to test matrix
* travis: remove old puppet versions from test matrix
* travis: add ruby 2.0 to test matrix
* git: show smarter diff for ruby files
* git: ensure ruby files have LF line endings
* README: improve markdown formatting
* README: show how to set chocolatey as default provider
* CONTRIBUTING: add instructions to contribute
* README: Use correct upstream build status for travis badge
* spec: protect against trailing whitespace

ps: The puppet forge still lists rismoney as the upstream at http://forge.puppetlabs.com/rismoney/chocolatey
but I notice that rismoney/puppet-chocolatey is now a fork of chocolatey/puppet-chocolatey 
Therefore I opened the PR here.