Modified setup to include spec file and debian/changelog in sdist tarball
This PR reworks setup.py in the following ways
- moved custom command definitions and utilities to
setup_utils.py, allowing for a slimmed-downsetup.pyscript (which is much more readable) - created new
bdist_specandchangelogcommands that are then called byegg_infoto create thegwpy.specanddebian/changelogfiles - these are required in the tarball that gets sent to software.ligo.org for LDG packaging, so this fixes #560 (closed)