Swift package localized resources

[ejensen]

This change updates the Swift package definition to support localized resources. This was done by following Apple's Localizing Package Resources article.

The pod spec has been updated to generate the resource bundle rather than using a pre-built bundle. The pre-built bundle is not recommended in CocoaPods:

For building the Pod as a static library, we strongly recommend library developers to adopt resource bundles as there can be name collisions using the resources attribute. Moreover, resources specified with this attribute are copied directly to the client target and therefore they are not optimised by Xcode.