gist.el doesn't use authsources

[paradoja]

As commented here #113 (comment) by @nickanderson , there's no (easy) way of having gist.el use already configured authsources (eg. .authinfo or .authinfo.gpg), and instead relies on reading and writing information directly in the global .gitconfig.

Ideally, if the token/password for github is already in .authinfo or similar, it should not be required to find the password or token in the .gitconfig.