Switch over to use PyGitHub for more capabilities

[astrochun]

We are using simple requests with the GitHub API. For improvements we should consider switching to PyGithub

[astrochun]

I managed to get PyGitHub installed and ran it and here are the timeit results.

In [2]: %timeit -n1 -r5 repo_list.get_repo_list('astrochun')                                                                                          
618 ms ± 298 ms per loop (mean ± std. dev. of 5 runs, 1 loop each)

In [3]: %timeit -n1 -r5 repo_list.get_repo_list_old('astrochun')                                                                                      
354 ms ± 210 ms per loop (mean ± std. dev. of 5 runs, 1 loop each)

Not surprisingly, for getting just metadata about repository, the old way is faster.