Make nokogiri dependency optional

Gemfile

@@ -9,5 +9,6 @@ group :development, :test do
   gem 'coveralls', require: false, platforms: [:mri]
 
   gem 'activerecord', '~> 4.1'
+  gem 'nokogiri', '~> 1.6'
   gem 'ox', '>= 2.1.2', platforms: [:mri, :rbx]
 end

README.md

@@ -28,30 +28,26 @@ $ bundle
 
 ## Usage
 
-To use **Nokogiri** as a SAX handler:
+SAX Machine can use either `nokogiri` or `ox` as XML SAX handler.
+
+To use **Nokogiri** add this line to your Gemfile:
 
 ```ruby
-require 'sax-machine'
+gem 'nokogiri', '~> 1.6'
 ```
 
-To use **Ox** as a SAX handler:
-
-Add this line to your application's Gemfile:
+To use **Ox** add this line to your Gemfile:
 
 ```ruby
 gem 'ox', '>= 2.1.2'
 ```
 
-Tell SAXMachine to use Ox:
+You can also specify which handler to use manually, like this:
 
 ```ruby
-require 'sax-machine'
-SAXMachine.handler = :ox
+SAXMachine.handler = :nokogiri
 ```
 
-Please note that this operation is not thread-safe, so it's better to define
-handler at initialization stage and do not change it during runtime.
-
 ## Examples
 
 Include `SAXMachine` in any class and define properties to parse:

lib/sax-machine.rb

@@ -14,4 +14,8 @@ def self.handler=(handler)
   end
 end
 
-SAXMachine.handler = :nokogiri
+begin
+  SAXMachine.handler = :ox
+rescue LoadError
+  SAXMachine.handler = :nokogiri
+end

sax-machine.gemspec

@@ -16,6 +16,5 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
   s.platform      = Gem::Platform::RUBY
 
-  s.add_dependency "nokogiri", "~> 1.6.0"
   s.add_development_dependency "rspec", "~> 3.0"
 end

spec/spec_helper.rb

@@ -14,9 +14,7 @@
 end
 
 require File.expand_path(File.dirname(__FILE__) + '/../lib/sax-machine')
-if ENV['HANDLER'] == 'ox'
-  SAXMachine.handler = :ox
-end
+SAXMachine.handler = ENV['HANDLER'].to_sym
 
 RSpec.configure do |config|
   config.run_all_when_everything_filtered = true