Introduce options to configure footer text

In site config =>
params:
  footer:
    text: "This is footer text - markdown suported"
    hideCopyright: true

closes: #1481

layouts/partials/footer.html

@@ -1,10 +1,19 @@
 {{- if not (.Param "hideFooter") }}
 <footer class="footer">
+    {{- if not site.Params.footer.hideCopyright }}
         {{- if site.Copyright }}
         <span>{{ site.Copyright | markdownify }}</span>
         {{- else }}
         <span>&copy; {{ now.Year }} <a href="{{ "" | absLangURL }}">{{ site.Title }}</a></span>
         {{- end }}
+        {{- print " · "}}
+    {{- end }}
+
+    {{- with site.Params.footer.text }}
+        {{ . | markdownify }}
+        {{- print " · "}}
+    {{- end }}
+
     <span>
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