Upgrade Octokit version to 2.x
Remove Octokit::Configuration::VALID_OPTIONS_KEYS

Because Octokit 2.0 use Octokit::Configurable.keys instead
Remove Client#authenticated? it's deprecated using Authentication#user_authenticated?
Lock compatible webmock version
Change request stubs for new Octokit 2.0 calls
oauth_token => access_token
Custom matcher for table listings
Custom matcher for table output
VCR for existing specs
Use login:token for better VCR compat