Astropy-package-template: try 2

This replaces #103.

@astrofrog - I don't know where this error comes from:
```
$ python setup.py test
Traceback (most recent call last):
  File "setup.py", line 65, in <module>
    get_debug_option(PACKAGENAME))
  File "/Users/adam/repos/spectral-cube/astropy_helpers/astropy_helpers/version_helpers.py", line 139, in generate_version_py
    last_generated_version = version_module.version
AttributeError: 'module' object has no attribute 'version'
```