Add configurable support for angled quotes

The flag `HTML_SMARTYPANTS_ANGLED_QUOTES` was added to Blackfriday on Black Friday. This configures rendering of double quotes as angled left and right quotes (&laquo;
&raquo;).

Typical use cases would be either or, or combined, but never in the same
document. As an example would be a person from Norway; he has a blog in both
English and Norwegian (his native tongue); he would then configure Blackfriday
to use angled quotes for the Norwegian section, but keep them as reqular
double quotes for the English.

This commit adds configuration support for this new flag, configuration that can be set in the site configuration, but overridden in page front matter.

Fixes #605
Added AuthorList, Author, AuthorSocial, SiteSocial, Image and Video structs
Added Page.Author(s) functions
Added schema, opengraph, twitter_cards, google_news metadata templates
Added "" template
Added top level .Hugo variable with version, commit and generator information + docs
Added Version, CommitHash and BuildDate to hugolib/hugo.go and used it in build
Removed commitHash and buildDate from commands/version.go and used hugolib vars
Removed getDateFormat function from commands/version.go
Trigger an editor after `hugo new`.

- Trigger permanently with NewContentEditor in config.{toml,yaml,json}.
- Trigger on an individual basis with --editor.
Use current working dir as WorkingDir instead of hugo executable's dir
feat(core): Add Tf-Idf page relevance scoring for related page graph.
doc(core): Add Related document feature documentation.
doc(core): go fmt
FECK
Added delimit & sort template functions, tests and docs
Hygiene: Reduce copy-pasted code.
Initialize funcMap in an init function.
Add a chomp function.

- Mostly useful in pipelines.
Implement `apply`.

- `map` is an alias function.
Commented helpers package
Add configuration option 'Title404'

Allow 'Title404' to be set for the title of the 404 page in config.*.
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.
Merge pull request #677 from derekperkins/seo-meta

Initial take on adding first class author, media and seo meta support

* derekperkins/seo-meta:
  Added AuthorList, Author, AuthorSocial, SiteSocial, Image and Video structs Added Page.Author(s) functions Added schema, opengraph, twitter_cards, google_news metadata templates Added "" template
Merge pull request #686 from bjornerik/feature/quotes-of-angles

Add configurable support for angled quotes

* bjornerik/feature/quotes-of-angles:
  Add configurable support for angled quotes

Conflicts:
	commands/hugo.go
	hugolib/shortcode.go