Support publishing vimwiki crate for web assembly

[chipsenkbeil]

This way, browsers could parse vimwiki within a page to provide syntax highlighting and other details.

Assuming macros feature would not be supported. HTML feature may also not be supported.

[chipsenkbeil]

Did a quick proof of concept and this works, although not without problems. I can parse and export a JavaScript object, but not my actual object because of the lifetime being required in the function. See rustwasm/wasm-bindgen#1187.

[chipsenkbeil]

Am able to apply syntax highlighting by providing a wasm function to return regions of headers (as js objects):

[chipsenkbeil]

Closing this out as it's now part of my active branch to introduce HTML support. The wasm API needs to be fleshed out, but that can be a separate issue.