Feature/instrumentation

I’m hoping this can be a collaborative effort between @colinmollenhour, @jonpday, @aedmonds and myself (Cc: @kyleterry for visibility). Could we use this pull request to review the proposed change and make improvements?

# Changes

* Refactored `log_broken_locks` into a `log_level` with standard levels (RFC-3164); deprecated `log_broken_locks`
* Adjusted log messages for clarity and changed level of existing log messages based on my understanding of severity
* Added debug loggers to aid developers in understanding the internals
* Added timing and compression instrumentation (at debug level) to aid developers

# Testing

* I haven’t yet tested _any_ of this, and I’m aware that’s in bad form (firing up a VM now…)