Added a convenience class for parsing HTML.

This removes the need for users having to set the `:html` option themselves.

lib/oga.rb

@@ -1,5 +1,8 @@
 require 'ast'
 
 require_relative 'oga/ast/node'
+
 require_relative 'oga/xml/lexer'
 require_relative 'oga/xml/parser'
+
+require_relative 'oga/html/parser'

lib/oga/html/parser.rb

@@ -0,0 +1,19 @@
+module Oga
+  module HTML
+    ##
+    # Low level AST parser for parsing HTML documents. See {Oga::XML::Parser}
+    # for more information.
+    #
+    class Parser < XML::Parser
+      ##
+      # @param [Hash] options
+      # @see Oga::XML::Parser#initialize
+      #
+      def initialize(options = {})
+        options = options.merge(:html => true)
+
+        super(options)
+      end
+    end # Parser
+  end # HTML
+end # Oga