Use requests instead of urllib for remote connections
This PR modifies the gwosc.api.fetch_json
function (the only thing that actually does any remote data access) to use requests.get
instead of urllib.request.urlopen
- it handles certificates and a bunch of other things better.
This actually resolves the appveyor issues that prompted #48,#50 in the first place.
This should resolve issues in the gwpy appveyor builds.