Add git tag for v0.1.8 and v0.1.9 releases

[tatsuya6502]

Hello @adrahon

It seems the repository on GitHub doesn't have tags for recent releases (v0.1.8 and v0.1.9). And also CHANGELOG.md is not updated after v0.1.5 release. It's a bit hard to me to figure out which release has which features and fixes.

Can you please add tags for v0.1.8 and v0.1.9 releases? Once it's done, I can update CHANGELOG.md by checking the commit log and GitHub issues, and then send a pull request to you.

Based on the release dates of the Ruby gem, I think you could tag to the following commits:

• 0.1.9 - August 27, 2014 - 96d9cf1
• 0.1.8 - August 5, 2014 - 20df572

Thank you,