Add validation to frameworks to make sure they are specified by name only

Tests are failing and I don't know why but I believe the logic makes
sense.
Make specs green.
Make code style linting green.
Add documentation and more specific error messages
Merge branch 'master' into Kapin-framework-linter-fix
Merge pull request #45 from CocoaPods/Kapin-framework-linter-fix

Add validation to frameworks to make sure they are only names