Improve visibility and usability of flushTraceLog()
I just went looking in the manual for how to force Projections logs out to disk at a defined point in my application code, and couldn't find it. I dug around and eventually found
flushTraceLog() in the header. This belongs in the manual, and should have a prototype in a standard header if it's not already. It should also have an empty definition for when there's no tracing bits linked in, so the user can call it without conditional compilation.
- Document it in the manual
- Add its prototype to a standard user-facing header, so it's always visible
- Implement a no-op version for when the real version isn't going to be linked