Setup/switch to astropy helpers

[wkerzendorf]

This is now an update to the new astropy setup helpers that make the update of any installation scripts much easier.

@ssim @orbitfold @mklauser can one of you sign off on this?

[wkerzendorf]

@embray @astrofrog - Hey guys, I've updated this package now to use the new package-template structure. It works really well and updating was a breeze!!! Thanks for that.

There are some minor issues that I still have. Currently running tests seems only possible for me using the following command line ASTROPY_USE_SYSTEM_PYTEST=1 python setup.py test --skip-docs

I think for most packages it would be great if they could use the system pytest if there is one installed. The other problem I ran into is

usage: -c [options] [file_or_dir] [file_or_dir] [...]
-c: error: unrecognized arguments: --doctest-rst

the only way to get rid of it is to use the command line option --skip-docs

If you guys could have a quick look that would be great.

[wkerzendorf]

@embray @astrofrog I fixed the doctest problem - there is now only the question how to enable the system pytest by default.

[ssim]

Sounds good to me!