Support Travis-CI

Add .travis.yml and put build-process on Rakefile for Integration with Travis-CI.

Please activation 'yury/ib' repository by following three step.

1. merge this pull request.
2. sign in with github account on Travis-CI
3. activate 'yury/ib' repo.

http://about.travis-ci.org/docs/user/getting-started/#Step-one%3A-Sign-in

Then, this repository is checked continuously by Travis-CI.

For example, my forked repo has success build on this pull request's commit.
https://travis-ci.org/ainame/ib/builds/12191120