spec style improve
ruby20 compability improve

1. ignore Gemfile.lock for multi ruby CI support
2. add ruby20 to travisCI
3. use 'bundler/gem_tasks' instead of jeweller
4. use rcov under ruby19
5. use simplecov in ruby19 & ruby20
Merge pull request #15 from crhan/ruby20

ruby20 compability improve
useless observablehash.rb