Left-align crate and release pages

Retain centered alignment for / and /about.

Since the crate page is navigated as part of a crate's documentation,
it's jarring for it to have different alignment than the documentation
itself.

Author: jsha

templates/about-base.html

@@ -1,5 +1,9 @@
 {% extends "base.html" %}
 
+{%- block body_classes -%}
+centered
+{%- endblock body_classes -%}
+
 {% block header %}
     <div class="docsrs-package-container">
         <div class="container">

templates/core/home.html

@@ -2,6 +2,10 @@
 
 {%- block title -%}Docs.rs{%- endblock title -%}
 
+{%- block body_classes -%}
+centered
+{%- endblock body_classes -%}
+
 {%- block body -%}
     <div class="container landing">
         <h1 class="brand">{{ "cubes" | fas(fw=true) }} Docs.rs</h1>

templates/style/style.scss

@@ -207,10 +207,13 @@ pre {
 
 div.container {
     max-width: 1160px;
-    margin: 0 auto;
     text-align: left;
 }
 
+body.centered div.container {
+    margin: 0 auto;
+}
+
 div.landing {
     text-align: center;
     padding-top: 30px;