Update cloudflare API lib and revise documentation

[m0ar]

Hello again :wave:

I figured out the token scoping issue related to the Worker metrics, I elaborated on this in the README and tidied it up in general. Also took the liberty of bumping cloudflare-go to the most recent version, it was lagging behind quite a bit.

Diff on the readme is a bit weird, better look at it rendered here.

Thanks for a great service, we finally have it rolling :confetti_ball: :beers:

[martinhaus]

@m0ar this is perfect! Thank you :)

[m0ar]

@martinhaus Would you mind pushing a new release to Docker Hub when you have the time? :revolving_hearts:

[martinhaus]

@m0ar just pushed it under the latest tag.