1.2.1

• The elements of the GrantTypes enum have been renamed to screaming snake case.
• A warning is raised, if a second TokenResource is created
  with a different token storage than the first one.
• Errors from txoauth2 are now real exceptions and should now be thrown instead of returned in
  OAuth2.onAuthenticate, TokenResource.onCustomGrantTypeRequest & ClientStorage.authenticateClient.
• ServerError now takes an optional message parameter.
• If the TokenFactory generates an invalid token,
  a ServerError is now returned instead of a ScopeError.
• TokenResource.getTokenStorageSingleton now raises a RuntimeError
  instead of a ValueError if no singleton was registered.
• TokenStorage.hasAccess must now also accept a single scope.
• Errors with 401 return code now always add a WWW-Authenticate header.
• Removed OAuth2RequestError and UnauthorizedOAuth2Error classes, these are now just OAuth2Errors.
• OAuth2Error got new optional parameters scope, addWwwAuthenticateHeader and authScheme.
• Renamed some attributes of the OAuth2Errors: message -> name, detail -> description.
• The position of the keyword argument state and errorUri switched for AuthorizationErrors
• Errors now validate their parameters. The OAuth2 spec only permits certain characters in the name,
  description, scope and errorUris. Any invalid characters will be replaced by a question mark.