Turn off comment caching for now

This should give a simple and obvious fix to the "Like" link
bug that was pointed out.  Given our current scale, along with
the following remark in the code,

; Comment caching doesn't make generation of comments significantly
; faster, but may speed up everything else by generating less garbage.

turning on comment caching seems like a premature optimization
that adds a lot of unnecessary complexity
Merge pull request #60 from machine-intelligence/feature/comment-caching-off

Turn off comment caching for now