Add log separator which can be recognised by external tools

[dkwach]

In current implementation whole log is send via one BLE message. It works if fit in MTU.
What in case when log is longer than MTU?

Consider defining logs_separator, which can be set in log streamer and potentially consumed by tools, which are collecting logs

[vovagorodok]

I can be logs_separator (disabled by default) option if is available than we merge only when this sign occurs