Sync meta in note contents.

Append metadata to note contents as meta tags.
The current format (in template form) is:

<mata name="<% key %>" value="<% JSON.stringify(value) %>">

To handle escaping issues, I'm using actual DOM elements for
encoding/decoding. This is likely slow but can be optimized later.

We could also use one meta tag instead of multiple, however, I feel that
multiple meta tags are the "canonical" way of doing this. Unfortunately,
we still need to encode the value as JSON to allow for booleans,
numbers, etc. This means string will look like '&quote;string&quote;'.

closes #57
Remove more dead code.
Include metadata in exported html.