Track document types when parsing.

When parsing XML/HTML documents the corresponding document type (:html or :xml)
is stored in Document#type.

spec/oga/xml/document_spec.rb

@@ -8,6 +8,10 @@ describe Oga::XML::Document do
 
       document.children[0].should == child
     end
+
+    example 'set the document type' do
+      described_class.new(:type => :html).type.should == :html
+    end
   end
 
   context '#children=' do

spec/oga/xml/parser/documents_spec.rb

@@ -11,6 +11,20 @@ describe Oga::XML::Parser do
     end
   end
 
+  context 'XML documents' do
+    before :all do
+      @document = parse('<foo></foo>')
+    end
+
+    example 'return a Document instance' do
+      @document.is_a?(Oga::XML::Document).should == true
+    end
+
+    example 'set the document type' do
+      @document.type.should == :xml
+    end
+  end
+
   context 'HTML documents' do
     before :all do
       html = <<-EOF.strip
@@ -31,6 +45,10 @@ describe Oga::XML::Parser do
       @document.is_a?(Oga::XML::Document).should == true
     end
 
+    example 'set the document type' do
+      @document.type.should == :html
+    end
+
     example 'set the doctype of the document' do
       @document.doctype.is_a?(Oga::XML::Doctype).should == true
     end