Always use RFC3339 for version date format.

Fixes #695 reported by @synful.

- No longer tries to load a configuration.
- Because of this the version tests are no longer necessary.
Remove Println that panics in test
Correct URL of the favicon in the documentation

img/favicon.png does not seem to exist,
so follow the example in docs/layouts/index.html
and use /favicon.ico instead.
Docs: Quote <!--more--> in <code> instead of italicizing it

Also replace "--" with "&#x2d;&#x2d;" prevent "--" from
being interpreted as en-dash.

Note: A simple `<!--more-->` does not work.
Docs: Minor copyediting/proofreading

- Correct some typos
- Add backticks and commas where necessary
- Use fenced code blocks specifying "bash" as the language
  to avoid weird highlighting
- Place commas outside of quotation marks surroundingn codes
  to avoid possible confusion
- Suggest users to use the discussion forum rather than the
  mailing list
Fix front matter for 'Creating a New Theme'

There seems to be an issue with TOML and certain menu structures. Current workaround: YAML.
Provide (relative) reference funcs & shortcodes.

-   `.Ref` and `.RelRef` take a reference (the logical filename for a
    page, including extension and/or a document fragment ID) and return
    a permalink (or relative permalink) to the referenced document.

    -   If the reference is a page name (such as `about.md`), the page
        will be discovered and the permalink will be returned: `/about/`
    -   If the reference is a page name with a fragment (such as
        `about.md#who`), the page will be discovered and used to add the
        `page.UniqueID()` to the resulting fragment and permalink:
        `/about/#who:deadbeef`.
    -   If the reference is a fragment and `.*Ref` has been called from
        a `Node` or `SiteInfo`, it will be returned as is: `#who`.
    -   If the reference is a fragment and `.*Ref` has been called from
        a `Page`, it will be returned with the page’s unique ID:
        `#who:deadbeef`.

-   `.*Ref` can be called from either `Node`, `SiteInfo` (e.g.,
    `Node.Site`), `Page` objects, or `ShortcodeWithPage` objects in
    templates.

-   `.*Ref` cannot be used in content, so two shortcodes have been
    created to provide the functionality to content: `ref` and `relref`.
    These are intended to be used within markup, like `[Who]({{% ref
    about.md#who %}})` or `<a href="{{% ref about.md#who %}}">Who</a>`.

-   There are also `ref` and `relref` template functions (used to create
    the shortcodes) that expect a `Page` or `Node` object and the
    reference string (e.g., `{{ relref . "about.md" }}` or `{{
    "about.md" | ref . }}`). It actually looks for `.*Ref` as defined on
    `Node` or `Page` objects.

-   Shortcode handling had to use a *differently unique* wrapper in
    `createShortcodePlaceholder` because of the way that the `ref` and
    `relref` are intended to be used in content.
Documentation for `ref` and `relref`.

- Rejigged the weight of the extras/ content for the new crossreferences
  page.
- Used the new {{%/*…*/%}} format for documenting highlighting and to
  prevent a warning about the missing `fig` shortcode.