* docs: unify nginx explainers and add apache httpd
there are two places where nginx + certbot is explained, unify that into
one place.
Add apache httpd, following the same steps, but using mod_md for
LetsEncrypt
add a note about #453 in both guides.
Link to both, and call the section reverse proxy, instead of NGINX
* restore full nginx.conf from docker.md
* add installation_guide/apache-httpd.md to mkdocs
* start centralizing negotiation logic for API
* swagger document nodeinfo endpoint
* go fmt
* document negotiate function
* use content negotiation
* tidy up negotiation logic
* negotiate content throughout client api
* swagger
* remove attachment on Content
* add accept header to test requests
* start experimenting with swagger documentation
* further adventures in swagger
* do a few more api paths
* account paths documented
* go fmt
* fix up some models
* bit o lintin'
