Swift Package Manager Support

[billbonney]

Hi.

This pull-request merges the current bug fixes and support for Swift Package Manager into a working code base.

You may consider merging the changes in a different order, but for now this works as reference for others looking for a working package with SPM support.

Hope this helps :) 👍

[hiroraba]

Hello @kylef.

I just wanted to let you know how much I appreciate your open-source project. It has proven to be incredibly useful and has become an essential tool for me.

As I plan to continue using it in the future, I would like to kindly request that you consider adding support for the Swift Package Manager. This would greatly enhance its usability and make it even more valuable for users like myself.

Thank you for your hard work and dedication to the project, and I look forward to seeing it continue to evolve.