Use .Site.Params.mainSections instead of hard coding "post" type

Hugo 0.32 or so added the quasi-magical .Site.Params.mainSections slice
that returns a range over the section that has the most number of pages.

This way we don't need to hard code the "post" type, and instead simply
use the pages that the user has created. Hugo's quickstart, for example,
recommends users create "posts", which currently doesn't work with this
theme!

Closes #89

layouts/_default/baseof.html

@@ -37,17 +37,10 @@
         <nav class="nav blog-nav">
           <a class="nav-link {{ if .IsHome }}active{{ end }}" href="{{ .Site.BaseURL | absLangURL }}">{{ i18n "home" }}</a>
           {{- $currentURL := .URL | absLangURL -}}
-          {{ if .Site.Params.custom_navbar }}
           {{ range .Site.Menus.navbar }}
           {{ $menuURL := .URL | absLangURL }}
           <a class="nav-link{{ if eq $menuURL $currentURL }} active{{ end }}" href="{{.URL | absURL }}">{{ .Name }}</a>
           {{ end }}
-          {{ else }}
-          {{ range where .Site.RegularPages "Type" "!=" "post" }}
-          {{ $permalinkURL := .Permalink | absLangURL }}
-          <a class="nav-link{{ if eq $permalinkURL $currentURL }} active{{ end }}" href="{{ .Permalink }}">{{ .Title }}</a>
-          {{ end }}
-          {{ end }}
         </nav>
       </div>
     </div>

layouts/_default/list.html

@@ -30,7 +30,7 @@
 {{ define "main" }}
 
 {{ $truncate := default true .Site.Params.truncate }}
-{{ $paginator := .Paginate (where .Data.Pages "Type" "post") }}
+{{ $paginator := .Paginate (where .Site.Pages "Section" "in" .Site.Params.mainSections) }}
 {{ range $paginator.Pages }}
 {{ if $truncate }}
 {{ .Render "summary" }}

layouts/partials/recent.html

@@ -2,7 +2,7 @@
     <h4>{{ i18n "recentPosts" }}</h4>
     <ol class="list-unstyled">
 {{ $num_recent_posts := (index .Site.Params.sidebar "num_recent_posts" | default 5) }}
-{{ range first $num_recent_posts (where .Site.RegularPages "Type" "post") }}
+{{ range first $num_recent_posts (where .Site.Pages "Section" "in" .Site.Params.mainSections) }}
 <li><a href="{{.RelPermalink}}">{{.Title | markdownify }}</a></li>
 {{ end }}
     </ol>