README: log

Brief

Logging services

Features

Usable in low-latency and realtime contexts
- Lock free
- No memory allocation
Performant (throughput comparable or better than third party solutions such as spdlog at default settings)
Reports timestamp and source location from where the log was fired
Threshold severity level settable at runtime
User definable log sinks (file, network, console)
User definable data format at sink
Simple API
```
log(severity, message);
```

Missing features:

Throttling (rate-limiting) based on location
Tools to filter logs by severity, location