feat: auto-load custom svg sprites from assets folder (#79)

BREAKING CHANGE: Build-in icons are prefixed with `gdoc_` now. If you use build-in icons in e.g. menus you have to rename these references!

layouts/partials/page-header.html

@@ -26,7 +26,7 @@
     {{ if (and (not $showBreadcrumb) (not $showEdit)) }} hidden {{ end }}" itemprop="breadcrumb">
     {{if $showBreadcrumb }}
     <div>
-        <svg class="icon path hidden-mobile"><use xlink:href="#path"></use></svg>
+        <svg class="icon gdoc_path hidden-mobile"><use xlink:href="#gdoc_path"></use></svg>
         <ol class="breadcrumb" itemscope itemtype="https://schema.org/BreadcrumbList">
             {{ $position := sub (len (split .RelPermalink "/")) 1 }}
             {{ $name := (partial "title" .) }}
@@ -38,7 +38,7 @@
     {{ if $showEdit }}
     <div>
         <span class="editpage">
-            <svg class="icon code"><use xlink:href="#code"></use></svg>
+            <svg class="icon gdoc_code"><use xlink:href="#gdoc_code"></use></svg>
             <a href="{{ $geekdocRepo }}/{{ $geekdocEditPath }}/{{ $.Scratch.Get "geekdocFilePath" }}">
                 Edit this page
             </a>