This allows defining JUCE_LOG_CURRENT_ASSERTION when using Visual
Studio, where escaping semicolons in the command-line is not possible.

This allows real-time threads to join an audio workgroup on Apple platforms.

Status codes are already filtered in curlHeaderCallback, so there's no
need to remove them again in parseHttpHeaders. Request headers will
never include a status, so there's no need to remove the status in that
case.

- macOS behaviour of setRealtime now matches other platforms

MR feedback

- added unit tests
- best performance timers used for each platform
- fixed an issue in which timer callbacks could drift