Update docs. Add use case. Add test.

README.md

@@ -215,10 +215,9 @@ Or if you have no site specific images simply:
 ```yml
 image:
   path: /img/banner.png
-  height: 100
-  width: 100
 ```
 
+> Using the image dimensions are optional, but the [Google Structured Data Testing Tool](https://search.google.com/structured-data/testing-tool/u/0/) will consider the JSON-LD to have errors when an image does not have specified dimensions.
 
 ### Setting a default image
 

lib/template.html

@@ -266,7 +266,7 @@
     },
 {% endif %}
 
-{% if seo_type == "BlogPosting" %}
+{% if seo_type == "BlogPosting" or seo_type == "CreativeWork" %}
     "mainEntityOfPage": {
          "@type": "WebPage",
          "@id": {{ page.url | replace:'/index.html','/' | absolute_url | jsonify }}

spec/jekyll_seo_tag_spec.rb

@@ -250,6 +250,16 @@ describe Jekyll::SeoTag do
       end
     end
 
+    context "with seo type is CreativeWork" do
+      let(:site) { make_site("url" => "http://example.invalid") }
+      let(:page) { make_post("seo" => { "type" => "CreativeWork" }, "permalink" => "/foo/") }
+
+      it "outputs the mainEntityOfPage" do
+        expect(json_data["mainEntityOfPage"]["@type"]).to eql("WebPage")
+        expect(json_data["mainEntityOfPage"]["@id"]).to eql("http://example.invalid/foo/")
+      end
+    end
+
     context "with site.title" do
       let(:site) { make_site("title" => "Foo", "url" => "http://example.invalid") }