- remove textile/pre processors from Resource::Text
    - streamline to allow domain-specific subclassing if needed

- initialize site by setting ivars directly, not by passing params to super's initialize()

- create alternate sites (beta, final, etc.) by subclassing site, and changing @output or @location
    - allow CLI option to specify site

- rework resource URI usage
    - 'uri' attribute should be canonical
        - 'output_file' should be derived from @site.output_dir + uri
    - URIs should be fully qualified
        - start with '/'
        - have extension according to file type
    - referencing URIs should follow server rules (e.g., / -> /index.html)
    - #shorten_uris should only apply to writing final files

- combine @input_file & @content?
    - if @content.kind_of?(Path): copy
    - else: write as string

- rename Resource #load to #import
    - uses path argument instead of @input_file
    - sets @content to path
    - sets @date to mtime of path
    - subclasses should:
        - call super
    - subclasses may:
        - assigned @content
        - change URI

- rename Resource #build to #process

- formalize widget creation & access
    - any object that responds to #to_html
    - doesn't have to be specific class (e.g., Mill::Widget)
    - object that is used across site
    - possibly with different states or parameters (eg, navigation)
    - built from current html_fragment use
    - eg:
        - navigation
        - buy buttons
        - Google Analytics bug
        - link to resource (<a ...>)
        - sidebars
        - strings (existing String extensions)

- 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

- 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)

- save compressed versions of files
    - write compressed versions along with non-compressed
    - serve compressed versions if asked by client