Enable HTTP/2 default

[lukeed]

Initially, sirv was meant to be a HTTP/2 server from the start, but there were some issues in setting this up. I think a lot of it may have to do with my incomplete knowledge of the H2 protocol, but in the early versions, I was seeing zero performance gain and, in some cases, saw worse performance. This is why I tabled it & sirv is now a(nother) HTTP/1 module.

This is relatively high priority. Because it requires Node 8 for the http2 module, this will also be a breaking change.

My plan of attack is to get sirv (as http) stable on 1.0 first. The http2 version can be made available on the next branch & npm tag until it's ready to become 2.0. At that point, I'll feel confident (enough) that it's done correctly this time around. 😅

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Revisit 3849356 and ed6cf05 for initial attempt.

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Module:

- [ ] Use createServer within sirv directly (again: 87b2d6d)
- [ ] Expect Buffer values for key & cert

• Lookup pushable assets from manifest via pathname

CLI Flags:

• --key, Path to SSL certificate key (Required)
• --cert, Path to SSL certificate file (Required)
• --cacert, Path to SSL certificate authority (Optional)
• -M --manifest, Path to HTTP/2 push manifest file

[lukeed]

(Mostly) Accessible in current @next release.
Preparing for 1.0 release soon.

This is done via sirv-cli only, which means that sirv still returns a middleware function.
This is made possible by Node.js directly – it ships a HTTP/2 Compatibility API, which means that the middleware signature is fine as is.

You pass file paths to the --key, --cert, and --cacert flags and they're handled accordingly to set up a HTTP/2 secure server.

Attaching manifest support (via route-manifest) is still on the agenda.

[lukeed]

Closed via #64