Contextual pull parsing.

This adds the ability to more easily act upon specific node types and nestings
when using the pull parsing API.

A basic example of this API looks like the following (only including relevant
code):

    parser.parse do |node|
      parser.on(:element, %w{people person}) do
        people << {:name => nil, :age => nil}
      end

      parser.on(:text, %w{people person name}) do
        people.last[:name] = node.text
      end

      parser.on(:text, %w{people person age}) do
        people.last[:age] = node.text.to_i
      end
    end

This fixes #6.

spec/oga/xml/cdata_spec.rb

@@ -33,4 +33,10 @@ describe Oga::XML::Cdata do
       @instance.inspect.should == 'Cdata(text: "foo")'
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :cdata
+    end
+  end
 end

spec/oga/xml/comment_spec.rb

@@ -33,4 +33,10 @@ describe Oga::XML::Comment do
       @instance.inspect.should == 'Comment(text: "foo")'
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :comment
+    end
+  end
 end

spec/oga/xml/doctype_spec.rb

@@ -63,4 +63,10 @@ Doctype(
       EOF
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :doctype
+    end
+  end
 end

spec/oga/xml/element_spec.rb

@@ -80,4 +80,10 @@ Element(
       EOF
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :element
+    end
+  end
 end

spec/oga/xml/node_spec.rb

@@ -13,4 +13,10 @@ describe Oga::XML::Node do
       described_class.new.children.should == []
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :node
+    end
+  end
 end

spec/oga/xml/pull_parser/context_parsing_spec.rb

@@ -0,0 +1,29 @@
+require 'spec_helper'
+
+describe Oga::XML::PullParser do
+  context '#on' do
+    before do
+      @parser = Oga::XML::PullParser.new('<a><b></b></a>')
+
+      @parser.stub(:node).and_return(Oga::XML::Text.new)
+    end
+
+    example 'do not yield if the node types do not match' do
+      expect { |b| @parser.on(:element, &b) }.to_not yield_control
+    end
+
+    example 'yield if the node type matches and the nesting is empty' do
+      expect { |b| @parser.on(:text, &b) }.to yield_control
+    end
+
+    example 'do not yield if the node type matches but the nesting does not' do
+      expect { |b| @parser.on(:text, %w{foo}, &b) }.to_not yield_control
+    end
+
+    example 'yield if the node type and the nesting matches' do
+      @parser.stub(:nesting).and_return(%w{a b})
+
+      expect { |b| @parser.on(:text, %w{a b}, &b) }.to yield_control
+    end
+  end
+end

spec/oga/xml/text_spec.rb

@@ -33,4 +33,10 @@ describe Oga::XML::Text do
       @instance.inspect.should == 'Text(text: "foo")'
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :text
+    end
+  end
 end

spec/oga/xml/xml_declaration_spec.rb

@@ -58,4 +58,10 @@ XmlDeclaration(
       EOF
     end
   end
+
+  context '#type' do
+    example 'return the type of the node' do
+      described_class.new.node_type.should == :xml_decl
+    end
+  end
 end