Added XML::Node#before and XML::Node#after

These methods can be used to insert nodes before/after other nodes without
manually having to mess around with node sets.

This fixes #28.

spec/oga/xml/node_set_spec.rb

@@ -196,6 +196,49 @@ describe Oga::XML::NodeSet do
     end
   end
 
+  context '#insert' do
+    before do
+      @set       = described_class.new
+      @owned_set = described_class.new([], Oga::XML::Node.new)
+    end
+
+    example 'insert a node into an empty node set' do
+      node = Oga::XML::Node.new
+
+      @set.insert(0, node)
+
+      @set[0].should == node
+    end
+
+    example 'do not insert a node that is already in the set' do
+      node = Oga::XML::Node.new
+
+      @set.insert(0, node)
+      @set.insert(0, node)
+
+      @set.length.should == 1
+    end
+
+    example 'insert a node before another node' do
+      node1 = Oga::XML::Node.new
+      node2 = Oga::XML::Node.new
+
+      @set.insert(0, node1)
+      @set.insert(0, node2)
+
+      @set[0].should == node2
+      @set[1].should == node1
+    end
+
+    example 'take ownership of a node when inserting into an owned set' do
+      node = Oga::XML::Node.new
+
+      @owned_set.insert(0, node)
+
+      node.node_set.should == @owned_set
+    end
+  end
+
   context '#[]' do
     before do
       @n1  = Oga::XML::Element.new(:name => 'a')

spec/oga/xml/node_spec.rb

@@ -178,4 +178,36 @@ describe Oga::XML::Node do
       @n1.node_set.nil?.should == true
     end
   end
+
+  context '#before' do
+    before do
+      @node      = described_class.new
+      @container = described_class.new(:children => [@node])
+    end
+
+    example 'insert a node before another node' do
+      other = described_class.new
+
+      @node.before(other)
+
+      @container.children[0].should == other
+      @container.children[1].should == @node
+    end
+  end
+
+  context '#after' do
+    before do
+      @node      = described_class.new
+      @container = described_class.new(:children => [@node])
+    end
+
+    example 'insert a node after another node' do
+      other = described_class.new
+
+      @node.after(other)
+
+      @container.children[0].should == @node
+      @container.children[1].should == other
+    end
+  end
 end