Swift Package Manager compatibility

[corteggo]

Code for #8

[corteggo]

This is what I've done here:

• Clean pods stuff from sample project to leverage git clone. You must update your CI to run pod install if it's not doing it at this moment.
• Add Swift Package Manager compatibility with Package.swift file.
• Swift/Objective-C classes mangling. I had to separete them in two different targets because SPM does not support mixed sources (and it won't).
• Checked your unit tests run properly after changes using CocoaPods.
• Tried to add a new sample project for SPM usage but I can't. SPM does not support adding duplicated resources for app and test targets.

In order to make this work for other users:

• You must merge this pull request.
• You must create a tag named 0.2.2 in your repository.

Hope it helps. Please do not hesitate to modify it as you want.