Icon and logo support with simple tests (#412)

Merge pull request 412

Author: ChaosKid42

README.md

@@ -33,6 +33,15 @@ The plugin will automatically use any of the following configuration variables,
 * `description` - A longer description of what your site is about, e.g., "Where I blog about Jekyll and other awesome things"
 * `url` - The URL to your site, e.g., `https://example.com`. If none is provided, the plugin will try to use `site.github.url`.
 * `author` - Global author information (see below)
+* `feed.icon` - Icon with 1:1 proportions for readers to use for the blog feed (not supported by all readers; often overridden by a favicon or site icon)
+* `feed.logo` - Logo with 2:1 proportions for readers to use for the blog feed (not supported by all readers). 
+  For example, both of the preceding can be expressed:
+  ```yml
+  feed:
+    icon: /images/icon.png
+    logo: /images/logo.png
+  ```
+
 
 ### Already have a feed path?
 

lib/jekyll-feed/feed.xml

@@ -27,6 +27,22 @@
     <subtitle>{{ site.description | xml_escape }}</subtitle>
   {% endif %}
 
+  {% if site.feed.icon %}
+    {% assign feed_icon = site.feed.icon %}
+    {% unless feed_icon contains "://" %}
+      {% assign feed_icon = feed_icon | absolute_url %}
+    {% endunless %}
+    <icon>{{ feed_icon | xml_escape }}</icon>
+  {% endif %}
+
+  {% if site.feed.logo %}
+    {% assign feed_logo = site.feed.logo %}
+    {% unless feed_logo contains "://" %}
+      {% assign feed_logo = feed_logo | absolute_url %}
+    {% endunless %}
+    <logo>{{ feed_logo | xml_escape }}</logo>
+  {% endif %}
+
   {% if site.author %}
     <author>
         <name>{{ site.author.name | default: site.author | xml_escape }}</name>

spec/jekyll-feed_spec.rb

@@ -125,6 +125,8 @@
       expect(feed.encoding).to eql("UTF-8")
       expect(feed.lang).to be_nil
       expect(feed.valid?).to eql(true)
+      expect(feed.icon).to be_nil
+      expect(feed.logo).to be_nil
     end
 
     it "outputs the link" do
@@ -238,6 +240,24 @@ def to_s
         expect(feed.title.content).to eql(site_title.encode(xml: :text))
       end
     end
+
+    context "with site.icon set" do
+      let(:site_icon) { "myicon.png" }
+      let(:overrides) { { "feed" => { "icon" => site_icon } } }
+
+      it "uses site.icon for the icon" do
+        expect(feed.icon.content).to eql("http://example.org/" + site_icon)
+      end
+    end
+
+    context "with site.logo set" do
+      let(:site_logo) { "mylogo.png" }
+      let(:overrides) { { "feed" => { "logo" => site_logo } } }
+
+      it "uses site.logo for the logo" do
+        expect(feed.logo.content).to eql("http://example.org/" + site_logo)
+      end
+    end
   end
 
   context "smartify" do