Add a Gemfile that reads from the gemspec

This lets you 'bundle install' to install required dependencies in
development.
Git ignore gem, ruby versions.
Add OAuth library support. More permissive gem versions.

* Faraday middleware to add the access_token in every request
* OAauth2 library for requesting the access_token
* Require major versions of gems only.
Use status code of response rather than body string for 401.
Fetch acc_token on first request; all requests include acc_token.

Also removed some rails-specific methods like Object#present? in favour
of plain ruby.
Spaces instead of tabs in lib/zoning/connection.
Connection#acc_token is now private.
Fix OAuth endpoint - hardcode production URL for now.

Will need to switch this based on another ENV to make it easier to
develop, support staging etc.
Remove .env.sample file from gem to reduce confusion.

This should be set in the application e.g. zoningcheck-rails. For
automated testing this will be handled internally anyway.
Greater flexibility with protocol, site url; read constants from config.

Constants like default locale and token path should be in the config
file in case we need them elsewhere and so all the config setting is in
one place.

Other constants are variable depending on whether we're in development,
test or production so should be read from ENV.
Support for specs.
Remove codeclimate support, add .travis.yml
Update rspec version in Rakefile to fix travis.
Some initial specs for Zoning::Connection.

Test-driving better handling of errors.
Error handling for access token fetch; specs pass.
Merge pull request #1 from opencounter/oauth

Support for the OAuth2 version of ZoningAPI