Define the Base Template and fix Hugo warnings

* Define the Base Template (baseof.html)
* Use relative URL link to style.css file
* Move summary.html from partials to _default layouts
* Fix Hugo warnings (needs Hugo 0.20 or newer)
* Fix Paginator rule on main page. Fix #8
* Latest posts: show pages from mainSections only
* Bump Hugo 0.19 -> 0.20
* Formatting

layouts/_default/single.html

@@ -1,4 +1,4 @@
-{{ partial "header.html" . }}
+{{ define "main" }}
 	<main>
 		<article>
 			<h1>{{ .Title }}</h1>
@@ -9,7 +9,7 @@
 			<div>
 				<ul id="tags">
 					{{ range .Params.tags }}
-					<li><a href="{{ "/tags/" | relLangURL }}{{ . | urlize }}">{{ . }}</a> </li>
+					<li><a href="{{ "/tags/" | relLangURL }}{{ . | urlize }}">{{ . }}</a></li>
 					{{ end }}
 				</ul>
 			</div>
@@ -19,4 +19,4 @@
 		</article>
 	</main>
 {{ partial "sidebar.html" . }}
-{{ partial "footer.html" . }}
+{{ end }}