Introduce configuration to allow build servers provided by the Travis CI
service to execute the test generation tool and commit the resultant
files to the canonical upstream repository.

Enabling this workflow required additional administrative work:

1. Create an account with TravisCI
2. Install the `travis` command-line utility
3. Create a "deploy key" and an encrypted version using the command
   `./make.py github_deploy_key_enc`
4. Register the deploy key with the project's GitHub account
5. Check the encrypted deploy key to the repository
6. Configure the TravisCI service to automatically build this project