Set Jekyll URL to https://pusher.github.io/oauth2_proxy

Created docs directory, split README contents into separate pages.

Do not infer username from email

fixing code redemption error string logging

build: use go 1.12 for arm as well

fix Docker user on arm

Use simple USER directive.
Using `addgroup` in final `arm` image when building on amd64 doesn't work.
I must have made a mistake during cross build verification.

Alternative is to use qemu-static but it's not worth it for this.

Added auth and standard logging with templating and file rolling

added jwt-key-file option

Update changelog for release v3.2.0

* build: use go 1.12

* Update CHANGELOG.md

Update Readme for Azure Active Directory

Co-Authored-By: martin-loetzsch <martin.loetzsch@gmail.com>

Co-Authored-By: martin-loetzsch <martin.loetzsch@gmail.com>