Removed lazy way of setting instance variables.

This process is quite a bit slower compared to setting instance variables
directly.

lib/oga/xml/doctype.rb

@@ -38,9 +38,11 @@ module Oga
       # @option options [String] :system_id
       #
       def initialize(options = {})
-        options.each do |key, value|
-          instance_variable_set("@#{key}", value) if respond_to?(key)
-        end
+        @name         = options[:name]
+        @type         = options[:type]
+        @public_id    = options[:public_id]
+        @system_id    = options[:system_id]
+        @inline_rules = options[:inline_rules]
       end
 
       ##

lib/oga/xml/document.rb

@@ -27,11 +27,9 @@ module Oga
       # @option options [Oga::XML::XmlDeclaration] :xml_declaration
       #
       def initialize(options = {})
-        options.each do |key, value|
-          instance_variable_set("@#{key}", value) if respond_to?(key)
-        end
-
-        @children ||= []
+        @children        = options[:children] || []
+        @doctype         = options[:doctype]
+        @xml_declaration = options[:xml_declaration]
       end
 
       ##

lib/oga/xml/element.rb

@@ -19,8 +19,19 @@ module Oga
     class Element < Node
       attr_accessor :name, :namespace, :attributes
 
-      def after_initialize
-        @attributes ||= {}
+      ##
+      # @param [Hash] options
+      #
+      # @option options [String] :name The name of the element.
+      # @option options [String] :namespace The namespace of the element.
+      # @option options [Hash] :attributes The attributes of the element.
+      #
+      def initialize(options = {})
+        super
+
+        @name       = options[:name]
+        @namespace  = options[:namespace]
+        @attributes = options[:attributes] || {}
       end
 
       ##

lib/oga/xml/node.rb

@@ -30,13 +30,10 @@ module Oga
       # @option options [Oga::XML::Node] :previous The previous node.
       #
       def initialize(options = {})
-        options.each do |key, value|
-          instance_variable_set("@#{key}", value) if respond_to?(key)
-        end
-
-        @children ||= []
-
-        after_initialize if respond_to?(:after_initialize)
+        @parent   = options[:parent]
+        @children = options[:children] || []
+        @next     = options[:next]
+        @previous = options[:previous]
       end
 
       ##

lib/oga/xml/text.rb

@@ -10,6 +10,17 @@ module Oga
     class Text < Node
       attr_accessor :text
 
+      ##
+      # @param [Hash] options
+      #
+      # @option options [String] :text The text of the node.
+      #
+      def initialize(options = {})
+        super
+
+        @text = options[:text]
+      end
+
       ##
       # @return [String]
       #

lib/oga/xml/xml_declaration.rb

@@ -26,12 +26,9 @@ module Oga
       # @option options [String] :standalone
       #
       def initialize(options = {})
-        options.each do |key, value|
-          instance_variable_set("@#{key}", value) if respond_to?(key)
-        end
-
-        @version  ||= '1.0'
-        @encoding ||= 'UTF-8'
+        @version    = options[:version] || '1.0'
+        @encoding   = options[:encoding] || 'UTF-8'
+        @standalone = options[:standalone]
       end
 
       ##