support ruby 1.8
support ruby 2.0
Merge branch 'ruby-2.0' into ruby-1.8

Conflicts:
	Gemfile
Merge branch 'master' into ruby-1.8
fix Document#thumbnails! specs for Ruby 1.8
Merge pull request #48 from p0deje/ruby-1.8

Support Ruby 1.8 and Ruby 2.0