Structure cleanup

As suggested in my other pull request, here is my cleanup with:
- More recent gemspec format
- A Gemfile
- Better rspec task
- Gitignore
- Simpler travis.yml
- License file
- Updated README with setup instructions and travis.ci badge
- Fixed indentation (only tabs)
- Reduced `sleep` in specs to make them quicker
- Bumped version to 0.2.0

Let me know if you have any suggestions.

---

BTW In case you didn't know, you can now use bundle's standard rake task to deal with gems:
```
$ ruby-thread (structure_cleanup) > rake -T
rake build    # Build thread-0.2.0.gem into the pkg directory
rake install  # Build and install thread-0.2.0.gem into system gems
rake release  # Create tag v0.2.0 and build and push thread-0.2.0.gem to Rubygems
rake spec     # Run RSpec code examples
```

For example, once you merged this, you can do `rake release` to tag the commit, build the gem and push it to rubygems automatically.