- resolve confusion between content-generation in #load vs. #final_content
    + who does what?
    + replacement/modification of HTML elements (image sizing, etc.) only happens in #load
    + maybe #final_content should have option to fully qualify URIs, etc., to handle feed content

- split Resource#date into Resource#published & Resource#updated
    + add <published> element to feed
    + #published should be stated date (e.g., from header)
    + #updated should be mtime of source file

- refactor MIME type usage
    + allow specified type as regexp or glob (use File.fnmatch?)
    + convert to MIME::Type object(s)

- make Navigator into more generic Collection
    + include Enumerable

- make Resource::External for external links?
    + add on import of HTML (by examining href/src/etc attributes)

- Rationalize resource URI usage:
    + #shorten_uris should only apply to writing final files.
    + In original content/etc., URIs should be more flexible.
    + A #convert_uris method should convert all references to proper type.

- Compress/minify Javascript, CSS, and HTML
    + https://remino.net/rails-html-css-js-gzip-compression/
    + http://sass-lang.com/documentation/file.SASS_REFERENCE.html#_16
    + JS: https://github.com/lautis/uglifier
    + HTML: https://github.com/paolochiodi/htmlcompressor
    + CSS: https://github.com/matthiassiegel/cssminify

- Write compressed versions along with non-compressed
    + Modify SimpleServer to use compressed versions if asked by client

- Add MailChimp signup form generator to HTMLHelpers.

- Add Google Analytics bug generator to HTMLHelpers and Mill setup.