fix(performance): comment all log_debug

[abrisse]

Hello @gkellogg,

While investigating some memory issues I discovered that the log_debug calls generate a lot of objects. Half of them were already commented so this PR comments all the others.

I did a small benchmark with memory_profiler:

allocated memory by gem (current)
-------------------------------------------------------
  48.30 MB  json-ld
  41.03 MB  rdf-ac80b2f2b82e

allocated memory by gem (with all log_debug commented)
-------------------------------------------------------
  43.33 MB  json-ld (- 10%)
  15.79 MB  rdf-ac80b2f2b82e (- 42%)

The 3 lines that stores a lot of objects:

• 9.12 MB rdf/util/logger.rb:181
• 7.97 MB rdf/util/logger.rb:224
• 6.98 MB rdf/util/logger.rb:180

This is partly because the RDF utils functions logger_debug / logger_common use splat operators which is quite costly, so I think the PR provide the best ROI.

[coveralls]

Coverage: 84.444% (-1.0%) from 85.432% when pulling 18f84e8 on PerfectMemory:fix/debug-log into 742eecb on ruby-rdf:develop.

[gkellogg]

Interesting and unfortunate. I've tried to decrease the impact of log_* calls by leaving costly evaluation in the block, but there's no good way to avoid splat arguments. I've gone back and forth about commenting out logging, and it can be useful when trying to debug gnarly corner-cases. But, the log_debug calls probably make up the bulk and shouldn't be as necessary to get basic algorithm tracing as log_info, for example.