Create podspec for cocoapods

* Moved JGDynamicSizeLabel to be with the rest of the source
* Updated podspec & added git tag to pass validation


I *think* this should be good to go for cocoapods however I'm not 100% sure. I don't know if this will push the tag as well which [cocoapods requires](https://github.com/CocoaPods/Specs#versioning).

Also, you might want to edit the podspec file as you see fit, I didn't fill in much of the author information but left it there commented out but removed quite a bit of the other comments. There are tons of options but I think it has enough as of now but if you want to you most definitely can.

Mostly just wanted to add cocoapods support since I use it for work & personal projects for dependency management. If you don't want to or don't like cocoapods feel free to just close this request.