www/caddy: os-caddy-1.6.1 (opnsense#579)

* www/caddy: Docs cleaned up for os-caddy-1.6.1

* www/caddy: caddy.rst add new features of os-caddy-1.6.1, improve overall layout.

* www/caddy: Add Basic Auth configuration example for completion. Simplify the simple setup even more. Improve structure for better readability.

* www/caddy: Add example Caddyfile for multiple handler structures.

Author: Monviech