Add a "custom" view example to the guide

[edenworky]

Basically, one writes a Haskell function that takes the Emanote model (all the data loaded from disk, the Pandoc AST, metadata, etc.) and returns the HTML for some page.

Originally posted by @srid in #141 (reply in thread)

This would also be great, not just on a per-page basis, but also on a per-section or per-embedding basis. I would love to help put together a PR with some guidance+pointers.

[srid]

@edenworky I believe that comment was referring to https://github.com/srid/emanima/

Add a "custom" view example to the guide

Yea, that's a good idea. FTR, here's the main part of it:

https://github.com/srid/emanima/blob/5c541274eda0a507895cdaf5b95554069d63457b/src/Emanima/Site.hs#L23-L43

Emanote uses Ema, which is where the 'composing' (of multiple sites, including Emanote sites) comes from. See https://ema.srid.ca/guide/compose

[srid]

Also, I'm working on extracting the core markdown parsing stuff out of Emanote into the ob library in https://github.com/srid/imako ... so one could use that as well. But ob is still in its fancy. Eventually, it will get to a point where I would use it in Emanote.