Add language-selector for multilingualism

[wasinski]

As I said it's not pretty. A lot of code is added just to have a | between menus and languages. I also tried to hide current language in the selector but I wasn't able to do it.

[luizdepra]

Could you provide the configuration required to use the multilingual feature?
I was unable to figure out how to show two (or more) languages alongside the menu.

Also, could you edit the README and explain how to use the feature?

[luizdepra]

And, please, add yourself into the Readme's contributors section.

[khos2ow]

Big +1 on the effort, I've done this on my own fork but haven't had the time to open a PR. Although I believe this PR requires a little bit of refactoring.

[khos2ow]

The href here can be written as {{ print "/" | absLangURL }}.

[khos2ow]

this whole block can be done as follow, IMO it's cleaner and without the repetition of language-selector.html:

<ul class="nav navbar-nav {{ if $.Site.Params.rtl }} navbar-left {{ else }} navbar-right {{ end }}">
  {{ with .Site.Menus.main }}
    {{ range sort . }}
      <li>
        <a href="{{ .URL | absLangURL }}">{{ i18n .Name }}</a>
      </li>
    {{ end }}
  {{ end }}

  {{ if .Site.IsMultiLingual }}
    {{ $node := . }}
    {{ .Scratch.Set "separator" true }}

    {{ range .Site.Home.AllTranslations }}
      {{ $language := printf "%s" .Language }}
      {{ if ne $.Site.Params.Langcode $language }}
        {{ if $node.Scratch.Get "separator" }}
          <li>
            <span>|</span>
          </li>
          {{ $node.Scratch.Set "separator" false }}
        {{ end }}
        <li>
          <a href="{{ .Permalink }}">{{ .Language.LanguageName }}</a>
        </li>
      {{ end }}
    {{ end }}
  {{ end }}
</ul>

I personally don't like the separator, but I added it here as an example (and it would be cool to make that configurable).

[wasinski]

@luizdepra README updated,
@khos2ow huge thanks!

[luizdepra]

Thank you.