General

• Update composer dependencies
• Update Travis-CI configuration

Refactoring

• Change Description::getBaseUrl() to Description::getBaseUri()
• Change Parameter::getRequired() to Parameter::isRequired()
• Change Parameter::getStatic() to Parameter::isStatic()

Updated to use Guzzle 6 and PSR-7.

• Event system has been replaced with a middleware system
• Move code from ProcessResponse to Deserializer
• Migrate ValidateInput to ValidateDescriptionHandler
• Change Description config option from baseUrl to baseUri
• Add request location FormParamLocation as substitute of PostFieldLocation
• Add request location MultiPartLocation as substitute of PostFileLocation
• Move methode HandleErrorResponses::handleError() to Deserializer:: handleErrorResponses()