feat(theme): support for series hint

- https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel#attr-next

source/_posts/caddy-nixos-part-1.md

@@ -8,6 +8,7 @@ tags:
 - linux
 - caddy
 - nixos
+series: first
 ---
 
 In this segment, I show you how I install NixOS.

source/_posts/caddy-nixos-part-2.md

@@ -8,6 +8,7 @@ tags:
 - linux
 - caddy
 - nixos
+series: true
 ---
 
 > 9 Nov 2020: Updated to NixOS 20.09 syntax.

source/_posts/caddy-nixos-part-3.md

@@ -9,6 +9,7 @@ tags:
 - caddy
 - nixos
 - cloudflare
+series: true
 ---
 
 > 9 Nov 2020: Updated to Caddy 2.1 syntax. Refer to {% post_link caddy-upgrade-v2-proxy 'this article' %} for upgrade guide.

source/_posts/i2p-eepsite-nixos.md

@@ -10,6 +10,7 @@ tags:
 - nixos
 - i2p
 - censorship
+series: last
 ---
 
 > 9 Nov 2020: Updated to Caddy 2.1 syntax. Refer to {% post_link caddy-upgrade-v2-proxy 'this article' %} for upgrade guide.

source/_posts/tor-hidden-onion-nixos.md

@@ -10,6 +10,7 @@ tags:
 - nixos
 - tor
 - censorship
+series: true
 ---
 
 > 9 Nov 2020: Updated to Caddy 2.1 syntax. Refer to {% post_link caddy-upgrade-v2-proxy 'this article' %} for upgrade guide.

themes/chameleon/layout/_partial/head.ejs

@@ -46,5 +46,21 @@ if (is_archive()) {
   <% if (theme.icons) { %>
     <%- css('/libs/forkawesome/css/forkawesome-1.1.7.min.css') %>
   <% } %>
+<% if (is_post() && page.series) { %>
+  <%
+  if (page.series !== 'first' && page.next?.path?.startsWith(`${config.archive_dir}/`)) {
+    const pageTitle = page.next.title
+  %>
+  <%/* page.next is not a typo */%>
+  <link rel="prev" href="<%- url_for(page.next.path) %>" title="<%= pageTitle %>">
+  <% } %>
+  <%
+  if (page.series !== 'last' && page.prev?.path?.startsWith(`${config.archive_dir}/`)) {
+    const pageTitle = page.prev.title
+  %>
+  <link rel="next" href="<%- url_for(page.prev.path) %>" title="<%= pageTitle %>">
+  <% } %>
+<% } %>
+
   <meta name="yandex-verification" content="e026a03a5dd06730" />
 </head>