Feature/carthage

[natalia-osa]

This fork introduces 3 elements:

1. Adds missing gitignore, to skip all user-generated data,
2. Makes init method of ARViewController public, so that it can be accessed normally,
3. Creates a framework, inside of which are all not-demo source files to tidy up & differ the demo/framework subprojects. The framework is shared, what makes the repo fully compatible with Carthage. I've tested the demo project and installation by Carthage. I did not test Cocoapods installation after this update (but it should work) and manual installation (where you'll surely need to modify the Readme).