feat: basic github style alerts support

layouts/_default/_markup/render-blockquote-alert.html

@@ -0,0 +1,20 @@
+{{- $supportedAlertTypes := slice "note" "tip" "important" "warning" "caution" -}}
+{{- $emojis := dict
+  "note" ":memo:"
+  "tip" ":bulb:"
+  "important" ":information_source:"
+  "warning" ":warning:"
+  "caution" ":exclamation:"
+-}}
+
+{{- if not (in $supportedAlertTypes .AlertType) -}}
+  <blockquote>
+    {{- .Text -}}
+  </blockquote>
+{{- else -}}
+  {{- $emoji := emojify (index $emojis .AlertType) -}}
+  {{- $content := .Text -}}
+  {{- $icon := "" -}}
+  {{- $class := "" -}}
+  {{- partial "shortcodes/callout.html" (dict "content" $content "emoji" $emoji "icon" $icon "class" $class) -}}
+{{- end -}}

layouts/_default/_markup/render-blockquote-regular.html

@@ -0,0 +1,3 @@
+<blockquote>
+  {{ .Text }}
+</blockquote>