Feature request: log to files

[rocketraman]

Sometimes it is useful to log on Android and iOS to files, which can easily be zipped up and transferred for remote analysis.

Now that kotlinx-io has been released and supports multiplatform filesystem writes (via okio, and works at least for most platforms including Android and iOS), it would be great if Kermit would leverage this to provide filesystem writing capability out of the box, rather than having users roll their own LogWriters.

For a logging tool, it would be useful also to support automatic roll-overs and deletion of older logs.