Capture ASL improvements

Continues work started by @Diarrhio in #242.

Main changes:

* Fix inverted log level and flag.
* Properly ignore messages with flag not matching captureLogLevel.
* No longer need for `DDASLLoggerIgnoreLogMessageTag`.
* No longer need to set async settings, now using default DDLog macros' settings.
* Fix Analyzer warning.
* Convert capture code to more standard 4-space indentation (sorry!).

Remaining issues:

- [ ] Capture is quite slow.