newest XCode throws warnings: This block declaration is not a prototype

[HerrSteiner]

Hi,

thanks for the STTwitter library. I got some warnings This block declaration is not a prototype for the library in a desktop project, I think it started with XCode 9.2. Most of them are easily to patch by applying the void in the empty declaration but some are not so easy to fix. I could provide my humble corrections in a pull request...