Fix support for Perlican 4

Uses keyword arguments for format()
diff --git a/templates/category.html b/templates/category.html
index d60326a..cfd4d2d 100644
--- a/templates/category.html
+++ b/templates/category.html
@@ -5,19 +5,19 @@
 
 {% block head %}
 {% if CATEGORY_FEED_ATOM %}
-<link href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_ATOM|format(category.slug) }}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} {{ category }} Category Atom Feed" />
+<link href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_ATOM|replace("{slug}", category.slug) }}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} {{ category }} Category Atom Feed" />
 {% endif %}
 {% if CATEGORY_FEED_RSS %}
-<link href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_RSS|format(category.slug) }}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} {{ category }} Category RSS Feed" />
+<link href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_RSS|replace("{slug}", category.slug) }}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} {{ category }} Category RSS Feed" />
 {% endif %}
 {% endblock %}
 
 {% block subheader %}
 <p>Category: {{ category }}
 {% if CATEGORY_FEED_ATOM %}
-&#124; <a href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_ATOM|format(category.slug) }}">Atom Feed</a>
+&#124; <a href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_ATOM|replace("{slug}", category.slug) }}">Atom Feed</a>
 {% endif %}
 {% if CATEGORY_FEED_RSS %}
-&#124; <a href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_RSS|format(category.slug) }}">RSS Feed</a>
+&#124; <a href="{{ FEED_DOMAIN }}/{{ CATEGORY_FEED_RSS|replace("{slug}", category.slug) }}">RSS Feed</a>
 {% endif %}</p>
 {% endblock %}
diff --git a/templates/tag.html b/templates/tag.html
index fef669a..de23d2b 100644
--- a/templates/tag.html
+++ b/templates/tag.html
@@ -5,19 +5,19 @@
 
 {% block head %}
 {% if TAG_FEED_ATOM %}
-<link href="{{ FEED_DOMAIN }}/{{ TAG_FEED_ATOM|format(tag.slug) }}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} {{ tag }} Tag Atom Feed" />
+<link href="{{ FEED_DOMAIN }}/{{ TAG_FEED_ATOM|replace("{slug}", tag.slug) }}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} {{ tag }} Tag Atom Feed" />
 {% endif %}
 {% if TAG_FEED_RSS %}
-<link href="{{ FEED_DOMAIN }}/{{ TAG_FEED_RSS|format(tag.slug) }}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} {{ tag }} Tag RSS Feed" />
+<link href="{{ FEED_DOMAIN }}/{{ TAG_FEED_RSS|replace("{slug}", tag.slug) }}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} {{ tag }} Tag RSS Feed" />
 {% endif %}
 {% endblock %}
 
 {% block subheader %}
 <p>Tag: {{ tag }}
 {% if TAG_FEED_ATOM %}
-&#124; <a href="{{ FEED_DOMAIN }}/{{ TAG_FEED_ATOM|format(tag.slug) }}">Atom Feed</a>
+&#124; <a href="{{ FEED_DOMAIN }}/{{ TAG_FEED_ATOM|replace("{slug}", tag.slug) }}">Atom Feed</a>
 {% endif %}
 {% if TAG_FEED_RSS %}
-&#124; <a href="{{ FEED_DOMAIN }}/{{ TAG_FEED_RSS|format(tag.slug) }}">RSS Feed</a>
+&#124; <a href="{{ FEED_DOMAIN }}/{{ TAG_FEED_RSS|replace("{slug}", tag.slug) }}">RSS Feed</a>
 {% endif %}</p>
 {% endblock %}