Rewrite project entirely

[leo]

This PR introduces serve-handler as the core of serve.

This is removing several command line flags (which were bloating the project), but also adding support for many more configuration options.

As a result, it makes serve more powerful, faster and more lean than ever before.

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NOTE: This is a fresh start. As mentioned above, a lot of features have been removed for which we couldn't find any reason to keep them as part of the core.

Once this is out, we'll re-evaluate every suggestion and see whether it makes sense to include it in serve itself, or if it makes more sense to just drop serve-handler into a 3-line .js file with micro in it and then add another middleware for the feature that you're looking for.

[vercel]

Changes in this PR will be automatically deployed with Now.

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[dawsbot]

I can hear the servers worldwide crying:

We should have pinned our major 😢

Our company has something like 20 separate frontend apps that all broke on this merge. Time to go fix them 1-by-1. Perhaps there's an announcement system to the create-react-app ecosystem on a change like this before it's done?

For reference, our command which now fails was "serve -s -t -p 5000 .". This is now met with "ERROR: Unknown or unexpected option: -t".