Add playground to readme

Add playground

Fix Dockerfile

Fix missing feature

Add support form GlobalPing monitor type, see #167

Add kuma CLI to the autokuma container, see #165

avoid boxed dyn refs

cleanup

fix unix socket support for docker source

Add Support for SMTP entity type, see #159

Added advanced docker host config for connecting to docker using TLS with custom certs, see #162

Fix resend_interval missing for most monitor types, see #152

Fix autokuma trying to use itself as a config file, see #149

Change 'upside_down' example from "bool" to "false"

Update README for setting key terminology