Add homepage property to gemspec.

- Set homepage as GitHub repository.
- Remove warning message from readme example.
Add version method and constant for project.

- Add version file and reference it via main file that includes class method to get VERSION constant.
- Update gemspec to get version from the application constant.
- Modify gemspec to include bindir attribute.
Ignore Mac OS X files in git.
Add Rakefile to handle common tasks for project.

- Add tasks to build, install, and uninstall the gem.
- Set default task to install.
- Add version constant that uses a lambda to get the version from the app.
- Add task to get the current version.
- Update readme with use of rake.