HTML docs

[diondokter]

Closes #87

Idea is:

• Generate multiple files, one per object (rustdoc style)
• With javascript, be able to convert bytes into field values and vice versa (calculator)
• Playground should be able to inspect the html but also render the html

Open questions:

• Should we just specify all doc comments are markdown and then render the markdown?
• Do we want to support no-js operations?
• What about search?
• Do we need a pdf-friendly version (so no calculator elements)?

Not everything needs to be done in this PR though.