Removed Gemfile.lock from version control.

The Gemfile.lock generally shouldn't be checked in for library-like projects. The
file is not suitable for bundling across implementations and platforms (eg Linux
vs Windows).
Added .travis.yml.
Ignore Rubinius compilation cache directory.
Added Gemfile.lock to .gitignore.
Removed ZenTest from Gemfile.

Attempting to bundle with ZenTest results in errors like the following:

Invalid gemspec in [/home/travis/.rvm/gems/ruby-1.9.3-p327/specifications/ZenTest-4.8.4.gemspec]: Illformed requirement ["< 2.1, >= 1.8"]

See eg https://travis-ci.org/brixen/shen-ruby/jobs/4917041
Re-add ZenTest. Requires rubygems 1.8.25.
Force Travis to update rubygems version.
Added rake to Gemfile for development.
Merge pull request #9 from brixen/master

Enable Travis CI running MRI 1.9, 2.0 and Rubinius 2.0