Live server shim/websocket customization

[soficshift]

Allows Ema users to specify the Ema Shim or a custom websocket response.

This can be used, for instance, to make the server open files in the user's favorite editor in response to a websocket request. So it could address #59, #69 (in some sense, since we can just use a custom shim).

[soficshift]

Rebased on top of #154

[soficshift]

Cool "page-following" demo with emacs and organon (using this PR).

cut.webm

[srid]

@lucasvreis Could you link me to your source that uses this feature (the custom shim as well as the custom renderer)? Just curious to see how it gets used, so I can understand the change better.

[soficshift]

@srid I've changed some things. Here is a more recent demo, at the end I explain how it works briefly:
video.webm

The code referenced in the video is here:
https://github.com/lucasvreis/organon/blob/48eb54a9b4026cff542ce5b4cf1a77b16d138b8f/organon/src/Site/Organon/Server.hs#L63-L81
https://github.com/lucasvreis/organon/blob/48eb54a9b4026cff542ce5b4cf1a77b16d138b8f/organon/src/Site/Organon/Dynamic.hs#L40-L52

I can explain the PR in matrix chat too, if you prefer.

[srid]

Whoa, nice demo! That makes me want to switch back (again) to org. 😁 Waiting for organon release ...

[soficshift]

Gravacao.de.tela.de.2023-02-21.19-36-03.webm

[srid]

@lucasvreis Does it make sense to simplify this example by upstreaming the SWITCH case (even if unused)? Because then we won't need to write a whole new shim, and can just use the default one. Only a custom server handler is defined.

[soficshift]

@srid I rebased on top of master and updated the second commit with your suggestion

[srid]

I really let this slip by. This weekend I'll spend some time merging this and other PRs, and then make a release of ema, emanote and relevant libraries.