It's worth noting:

https://github.com/mholt/caddy/blob/master/server/server.go

That the actual web server in use is:

https://github.com/bradfitz/http2

Which isn't to detract from the Caddy project which offers a tidy set of configuration options so that the lib is more like an Nginx executable with config files.

Perhaps the README can be updated though, as "Caddy binaries are available for nearly every platform and has no dependencies" is a bit misleading. The binary produced by Go may not have dependencies, but the Go code itself has a few large dependencies.