Move extractor from `scripts` to `data_files`.

`scripts` is meant to be for Python scripts:
> Scripts are files containing Python source code, intended to be
> started from the command line.
https://docs.python.org/2/distutils/setupscript.html#installing-scripts

The extractor is not a Python script and as thus isn't a good fit for
being listed under `scripts`. It doesn't seem to fall into any of the
other categories, which makes it fall into the category of files
`data_files` is meant for:
> The `data_files` option can be used to specify additional files needed
> by the module distribution: configuration files, message catalogs,
> data files, anything which doesn’t fit in the previous categories.
https://docs.python.org/2/distutils/setupscript.html#installing-additional-files

Fixes #24.