code: public Mail templateMessage(String template, Map<String, Object> content) throws MangooTemplateEngineException {
          Objects.requireNonNull(template, Required.TEMPLATE.toString());
          Objects.requireNonNull(content, Required.CONTENT.toString());
  
          if (template.charAt(0) == '/' || template.startsWith("\\")) {
              template = template.substring(1, template.length());
          } 
          
          this.email.htmlMessage(
                  Application.getInstance(TemplateEngine.class).renderTemplate(new TemplateContext(content).withTemplatePath(template)),
                  Default.ENCODING.toString());
  
          return this;
      }
docs: Sets a template to be rendered for the email. Using a template
  will make it a HTML Email by default.
  
  @param template The template to use
  @param content The content for the template
  @return A mail object instance
  @throws MangooTemplateEngineException if rendering of template fails