Add official support to Goth >= 1.3

[ulissesalmeida]

The PR is a suggestion in how we could offically support Goth >= 1.3.

Basically, the Goth >= 1.3, the user's app need to start a process that
will fetch and own a token. To be fair, this library doesn't need to do
much to transit to Goth 1.3 thanks to the Token Fetcher behaviour.

So this PR make changes to make the library use Goth >= 1.3 as
an example, update the Readme, and now requires the library to
suppliy a token fetcher module.

[petermueller]

when you get a chance, could you rebase? I mainly just wanna confirm all the tests work w/ the different versions. I don't see why they wouldn't though?

[fastjames]

Hi all, I noticed in the failing test (OTP 24) that for some reason the jose dependency was still at 1.10.1. I think that's the source of the calls to poly1305 that were removed in OTP24. I pulled the branch locally and ran

mix deps.update jose

and that updated the dep to 1.11.6. The update appeared to clear those errors.

[fastjames]

Hi all, I noticed in the failing test (OTP 24) that for some reason the jose dependency was still at 1.10.1. I think that's the source of the calls to poly1305 that were removed in OTP24. I pulled the branch locally and ran

mix deps.update jose

and that updated the dep to 1.11.6. The update appeared to clear those errors.

The library update appears to work standalone, so I opened a separate PR for it: #6 .