Update feeds fragment, add support for every feed-related variables

All this boilerplate is taken straight from the pelican simple theme:
- https://github.com/getpelican/pelican/blob/master/pelican/themes/simple/templates/base.html

templates/fragments/feeds.html

@@ -1 +1,24 @@
-<link rel="alternate" type="application/atom+xml" title="{{ SITENAME }} (Feed)" href="{{ FEED_DOMAIN }}/{{ FEED_ALL_ATOM }}" />
+{% if FEED_ALL_ATOM %}
+<link href="{{ FEED_DOMAIN }}/{% if FEED_ALL_ATOM_URL %}{{ FEED_ALL_ATOM_URL }}{% else %}{{ FEED_ALL_ATOM }}{% endif %}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} Full Atom Feed" />
+{% endif %}
+{% if FEED_ALL_RSS %}
+<link href="{{ FEED_DOMAIN }}/{% if FEED_ALL_RSS_URL %}{{ FEED_ALL_RSS_URL }}{% else %}{{ FEED_ALL_RSS }}{% endif %}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} Full RSS Feed" />
+{% endif %}
+{% if FEED_ATOM %}
+<link href="{{ FEED_DOMAIN }}/{%if FEED_ATOM_URL %}{{ FEED_ATOM_URL }}{% else %}{{ FEED_ATOM }}{% endif %}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} Atom Feed" />
+{% endif %}
+{% if FEED_RSS %}
+<link href="{{ FEED_DOMAIN }}/{% if FEED_RSS_URL %}{{ FEED_RSS_URL }}{% else %}{{ FEED_RSS }}{% endif %}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} RSS Feed" />
+{% endif %}
+{% if CATEGORY_FEED_ATOM and category %}
+<link href="{{ FEED_DOMAIN }}/{% if CATEGORY_FEED_ATOM_URL %}{{ CATEGORY_FEED_ATOM_URL.format(slug=category.slug) }}{% else %}{{ CATEGORY_FEED_ATOM.format(slug=category.slug) }}{% endif %}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} Categories Atom Feed" />
+{% endif %}
+{% if CATEGORY_FEED_RSS and category %}
+<link href="{{ FEED_DOMAIN }}/{% if CATEGORY_FEED_RSS_URL %}{{ CATEGORY_FEED_RSS_URL.format(slug=category.slug) }}{% else %}{{ CATEGORY_FEED_RSS.format(slug=category.slug) }}{% endif %}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} Categories RSS Feed" />
+{% endif %}
+{% if TAG_FEED_ATOM and tag %}
+<link href="{{ FEED_DOMAIN }}/{% if TAG_FEED_ATOM_URL %}{{ TAG_FEED_ATOM_URL.format(slug=tag.slug) }}{% else %}{{ TAG_FEED_ATOM.format(slug=tag.slug) }}{% endif %}" type="application/atom+xml" rel="alternate" title="{{ SITENAME }} Tags Atom Feed" />
+{% endif %}
+{% if TAG_FEED_RSS and tag %}
+<link href="{{ FEED_DOMAIN }}/{% if TAG_FEED_RSS_URL %}{{ TAG_FEED_RSS_URL.format(slug=tag.slug) }}{% else %}{{ TAG_FEED_RSS.format(slug=tag.slug) }}{% endif %}" type="application/rss+xml" rel="alternate" title="{{ SITENAME }} Tags RSS Feed" />
+{% endif %}

templates/sidebar.html

@@ -35,7 +35,7 @@
 					</a>
 				{% endif %}
 			{% endfor %}
-			<a class="sidebar-nav-item" href="{{ FEED_DOMAIN }}/{{ FEED_ALL_ATOM }}">
+			<a class="sidebar-nav-item" href="{{ FEED_DOMAIN }}/{{ FEED_ALL_ATOM if FEED_ALL_ATOM else FEED_ALL_RSS }}">
 				<i class="fas fa-rss"></i>
 			</a>
 		</nav>