Resolve callable classes
Resolve callable classes

Update CallableResolver to check if the string to resolve is in the
container or a class that can be invoked.

jaapverloop/Slim,feryardiant/slim,designermonkey/Slim,foxyantho/Slim,slimphp/Slim,AndrewCarterUK/Slim,mnapoli/Slim,iinux/Slim,dopesong/Slim,iinux/Slim,iinux/Slim,Sam-Burns/Slim,JoeBengalen/Slim,akrabat/Slim,juliangut/Slim,RealSelf/Slim