first crack at a summary.log

besides sending the summary stdout, it will also be logged to
(configurable) summary.log

Values:
```
{
  pid,
  timestamp,
  name = bid.summary,
  args[{
    agent, api, code, error, host, v, assertion_verification_time
  }]
 // plus others from intel, such as log level = INFO, etc
}
```
fixes #24 ?