Introduced configuration file for travis-ci.org.

Refs #4
Here is an example of what is generated if `with_tox` is selected too:

```yaml
language: python
env:
  - TOXENV=py27
  - TOXENV=py33
  - TOXENV=py34
  - TOXENV=flake8
  - TOXENV=readme
install:
  - make develop
script:
  - make test
```