Refactor active parts into a Swift Package Manager distribution. Add a CLI wrapper.

[adam-zethraeus]

This is cool! I didn't know the APIs were available. I'd have guessed you'd have to package tesseract.
I wanted a version I could build easily from the command line so I could add it to my cross-machine synced setup.

Feel free to ignore, take pieces, etc.

Changes:

• use swift package manager
• refactored to keep only the active parts
• added a CLI arguments wrapper
• removed the default pbcopy behaviour
• added --copy or -c flag to copy to clipboard
• made errors write to stderror and return a failed exit status
• make the script delete the temporary image