Remove the Document subclass, use the Metadata include

lib/dimples/page.rb

@@ -1,8 +1,21 @@
 # frozen_string_literal: true
 
-require_relative 'document'
-
 module Dimples
-  class Page < Document
+  # A class representing a single page on a site.
+  class Page
+    include Metadata
+
+    def initialize(path: nil, metadata: {})
+      @path = path
+      @metadata = {}
+      @contents = ''
+
+      load_metadata(path) if path
+      @metadata.merge!(metadata) unless metadata.empty?
+    end
+
+    def layout
+      @metadata.fetch(:layout, 'page')
+    end
   end
 end

lib/dimples/post.rb

@@ -1,11 +1,14 @@
 # frozen_string_literal: true
 
-require_relative 'document'
-
 require 'date'
 
 module Dimples
-  class Post < Document
+  # A class representing a single post on a site.
+  class Post < Page
+    def categories
+      @metadata.fetch(:categories, [])
+    end
+
     def date
       @metadata.fetch(:date, DateTime.now)
     end

lib/dimples/template.rb

@@ -1,8 +1,13 @@
 # frozen_string_literal: true
 
-require_relative 'document'
-
 module Dimples
-  class Template < Document
+  # A class representing a single template used for a layout on a site.
+  class Template
+    include Metadata
+
+    def initialize(path:)
+      @path = path
+      load_metadata(path)
+    end
   end
 end