{#-
  CSRF hidden input for state-changing POST forms. Usage:

      {% import "partials/csrf_field.html" as csrf %}
      <form method="post" action="...">
        {% call csrf::field(csrf_token) %}
        ...
      </form>
-#}
{%- macro field(token) -%}
<input type="hidden" name="csrf_token" value="{{ token }}">
{%- endmacro -%}
