Add Dynamic Framework support & Carthage support

[Jeehut]

This pull request adds iOS, tvOS and OSX targets with shared schemes (for installation via Carthage) and configures those to work as a dynamic framework. Also a section to the README about Carthage installation was added.

This should solve #8.

[Jeehut]

For the time being you can put github "Dschee/AERecord" "feature/framework-support" into your Cartfile and run carthage update until this is merged and a new version is released (with a tag named '2.0.1' or 'v2.0.1').

[Jeehut]

I just tried using my branch included as a framework, but at least when running tests there were issues with both finding the correct bundle(Identifier) (this one I tried to fix in the last commit) and creating an entityDescription object (probably cause entityName was wrong). So there seem to be a few path issues with Framework inclusion left as TODOs for it to work.

@tadija I think you're the best person for fixing that issues without breaking the current logic. Would you mind having a look?

[tadija]

Hi @Dschee, thanks for this temporary solution, I finally did this in 3.0.0.