feat: "Inline" Bridgetown

[jaredcwhite]

I'm looking at: https://starters.wolfgangrittner.dev/scripts

And I'm realizing how unbelievably awesome it would be if you could create a new Bridgetown app in a single file. Certainly not something for production use, but for quick one-offs to test things out—especially if you pair that with cloud editors—whoa. 🤯