v0.4.0

Metrics

A new Metrics tab shows an app's last hour or day: requests a minute
with the 5xx answers among them, CPU, memory and network traffic in and
out, with the crashes of the last day. The proxy counts the requests;
readings are taken once a minute and kept for a day.

The app header adds requests a minute, the share of server errors over
the last five minutes, and crashes today.