• BREAK: Renamed AbstractProvider::ACCESS_TOKEN_METHOD_GET to AbstractProvider::METHOD_GET.
• BREAK: Renamed AbstractProvider::ACCESS_TOKEN_METHOD_POST to AbstractProvider::METHOD_POST.
• BREAK: Renamed AbstractProvider::prepareUserDetails() to AbstractProvider::createUser().
• BREAK: Renamed AbstractProvider::getUserDetails() to AbstractProvider::getUser().
• BREAK: Removed $token parameter from AbstractProvider::getDefaultHeaders().
• BREAK: Modify AbstractProvider::getBaseAccessTokenUrl() to accept a required array of parameters, allowing providers the ability to vary the access token URL, based on the parameters.
• Removed newline characters from MAC Authorization header.
• Documentation updates, notably:
  • Moved list of providers to README.PROVIDERS.md.
  • Moved provider creation notes to README.PROVIDER-GUIDE.md.