title: Call nunjucks template macro using variable name
body: <p>Given a macro:</p>
  
  <pre><code>{% macro foo() %}
  {% endmacro %}
  </code></pre>
  
  <p>Is there a way to call it using a variable name:</p>
  
  <pre><code>{% set fn = 'foo' %}
  ... call macro using 'fn'
  </code></pre>
  
  <p>Alternatively how can I call a macro from a custom tag? I have created a tag that can accept these variables but not sure how to insert a macro from there.</p>