Allow adding SVG in place of logo image (adityatelange#976)

Usage =>
Params.label.iconSVG: "<your SVG as a string>"

Author: icy-comet

assets/css/common/header.css

@@ -27,7 +27,7 @@
     font-weight: 700;
 }
 
-.logo a img {
+.logo a img, .logo a svg {
     display: inline;
     vertical-align: middle;
     pointer-events: none;

layouts/partials/header.html

@@ -66,6 +66,8 @@
                 <img src="{{- site.Params.label.icon | absURL -}}" alt="" aria-label="logo"
                     height="{{- site.Params.label.iconHeight | default "30" -}}">
                 {{- end -}}
+                {{- else if hasPrefix site.Params.label.iconSVG "<svg" }}
+                    {{ site.Params.label.iconSVG | safeHTML }}
                 {{- end -}}
                 {{- $label_text -}}
             </a>