Found them installed in my `site-packages`, importable as `import tests` 😱
Tested with:
```
In [2]: find_packages()
Out[2]: ['tests', 'yamllint', 'tests.rules', 'yamllint.rules']
In [3]: find_packages(exclude=['tests', 'tests.*'])
Out[3]: ['yamllint', 'yamllint.rules']
```
As someone said [1] on the internet:
Say ".yaml" not ".yml".
This is not MS-DOS, and YML is a Yahoo XML dialect.
Similarly, we use '.json', not '.jsn'.
[1]: https://github.com/ceph/s3-tests/commit/e17c56a
Put `tests/yaml-1.2-spec-examples/*` back in `setup.py`'s `package_data`
because they need to be installed when running `python setup.py build`,
so Debian packaging script `dh_auto_test -O--buildsystem=pybuild`
doesn't fail.
See also commit e6dc67f.
`yamllint/conf/*.yml` remains in `setup.py`'s `package_data` because it
needs to be installed when running `pip install .`.
`docs/*` and `tests/yaml-1.2-spec-examples/*` just need to be packaged,
they can go in the manifest.
The `pyyaml` dependency is needed in `install_requires` but also in
`setup_requires`, because running `setup.py` requires importing
`yamllint`, which itself imports `yaml`.
