Alertmanager URI might contain basic auth username & password, we should replace password with 'xxx' in logs and and error messages.
Go will still print it in HTTP request errors, but that will be fixed in the next Go release - https://go-review.googlesource.com/c/go/+/102855Fixes#259
Internal packages are supported by Go 1.5+, any package in /internal/ dir is only importable from the same repo. This will cleanup main dir a bit and provide better namespace for unsee subpackages