Serde support for Event

[not-my-profile]

I'd like to access the events from Jotdown in JS (via WASM) as JSON. Would you accept a PR to implement optional serde support?

(basically adding #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] to Event and Container)

(precedent for serde support in a markup parser is given by pulldown-cmark having optional serde support)

[hellux]

Sure, I think it could be useful, and it is easy to feature-gate. Just like events, the resulting JSON may have breaking changes between 0.x releases so the format can be considered unstable at least for the time being. We have previously discussed serde/JSON support for an AST in #17, but this shouldn't conflict with that. A `serde` feature should be good for now to enable serde for events and containers. If we later add an AST, its serde support can be built by enabling both the `serde` and `ast` features.

[not-my-profile]

Closing this, I have since realized that the Event type isn't fine-grained enough for my use case: #78.