Maktaba should offer a simple log handler

Maktaba's logging is useful, but unless I'm missing something, there's easy no way to use it out of the box, as you need your own log handler before it'll do anything.

We don't want to install a log handler by default, but it would be useful to provide an optional `maktaba#log#InstallSimpleLogHandler()` that adds a handler that accumulates log records into a (user-specified?) limited-size list, along with a `maktaba#log#GetSimpleLogHandlerRecords()` or similar.