feat: more flexible hooks system

1. Use more standard hook names:
- head-start
- head-end
- body-end
- footer-start
- toc-start
- toc-end

2. Enable multiple files per hook. For example, a starter template may have `hooks/head-end/tpl.html` and a user may have customizations in `hooks/head-end/user.html`

custom_head.html -> hooks/head-end/custom.html
custom_js.html -> hooks/body-end/custom.html

Deprecates custom_head.html and custom_js.html but they remain supported for now.

wowchemy/layouts/partials/book_layout.html

@@ -12,15 +12,15 @@
     {{/* Show ToC by default. */}}
     {{ if ne .Params.toc false }}
     <div class="d-none d-xl-block col-xl-2 docs-toc">
-      {{ partial "hooks/page_toc_start" . }}
+      {{ partial "functions/get_hook" (dict "hook" "toc-start" "context" .) }}
 
       <ul class="nav toc-top">
         <li><a href="#" id="back_to_top" class="docs-toc-title">{{ i18n "on_this_page" }}</a></li>
       </ul>
 
       {{ .TableOfContents }}
 
-      {{ partial "hooks/page_toc_end" . }}
+      {{ partial "functions/get_hook" (dict "hook" "toc-end" "context" .) }}
     </div>
     {{ end }}
 

wowchemy/layouts/partials/functions/get_hook.html

@@ -0,0 +1,18 @@
+{{/* Function to inject custom code into layouts without overriding files. */}}
+{{/* Input: hook folder name (str) */}}
+{{/* Output: loaded (bool) */}}
+
+{{ $loaded := false }}
+{{ $partial_dir := printf "hooks/%s/" .hook }}
+{{ $hook_dir_path := path.Join "layouts/partials" $partial_dir }}
+{{ if fileExists $hook_dir_path }}
+  {{ range os.ReadDir $hook_dir_path }}
+    {{ if not .IsDir }}
+      {{ $partial_path := path.Join $partial_dir .Name }}
+      {{ partial $partial_path . }}
+      {{ $loaded = true }}
+    {{ end }}
+  {{ end }}
+{{ end }}
+{{/* The return statement below is for debug purposes only and prevents the above partial(s) being included in the page */}}
+{{/* return $loaded */}}

wowchemy/layouts/partials/site_footer.html

@@ -1,6 +1,6 @@
 <footer class="site-footer">
 
-  {{ partial "hooks/footer" . }}
+  {{ partial "functions/get_hook" (dict "hook" "footer-start" "context" .) }}
 
   {{ if .IsTranslated | and site.Params.footer.show_translations }}
     <div class="powered-by d-flex flex-wrap pb-2 justify-content-center">

wowchemy/layouts/partials/site_head.html

@@ -9,6 +9,9 @@
     <meta name="generator" content="Wowchemy {{ site.Data.wowchemy.version }} for Hugo" />
   {{ end }}
 
+  {{/* EXTENSIBILITY HOOK: HEAD-START */}}
+  {{ partial "functions/get_hook" (dict "hook" "head-start" "context" .) }}
+
   {{ if .Params.private }}
     <meta name="robots" content="noindex" />
   {{- end -}}
@@ -305,7 +308,13 @@
 
   {{ partial "jsonld/main" (dict "page" . "summary" $desc) }}
   {{ partial "cookie_consent" . }}
-  {{ partial "custom_head" . }}
 
   <title>{{$title}}</title>
+
+  {{/* EXTENSIBILITY HOOK: HEAD-END */}}
+  {{/* Deprecated custom_head hook */}}
+  {{ if templates.Exists "partials/custom_head" }}
+    {{ partial "custom_head" . }}
+  {{ end }}
+  {{ partial "functions/get_hook" (dict "hook" "head-end" "context" .) }}
 </head>