Default scope for --metrics that includes hostname, app name, and worker id

 * Adds internal support for %a and %h as expanders for appName and hostname
 * Fixes the poorly named logname module and generate function
 * Uses `'%a.%h.%w'` as default scope when the `--metrics` url does not provide one

@sam-github PTAL
line above "scope is optional and defaults to none", now it defaults to "%a.%h.%w", right?