Release tarball needs spec file and changelogs
In order to get the package released as a system package on the LIGO Data Grid, we need to upload a tarball to software.ligo.org, @skymoo has provided a script to do that which can be integrated into the deploy step of the travis CI.
But, the release tarball needs to include everything needed to build the RPM and deb packages, namely
gwpy.specdebian/changelog
both of which are built on-the-fly currently. So, we probably need to subclass sdist to include create those files and include them in the tarball.