Don't store Compare in Classifier + more tidbits.
Don't store Compare in Classifier + more tidbits.

This commit ensures that a comparison function is always passed to every
function, but never explicitly stored. It seems to generate a better
assembly output.

There are several other minor things: less template parameters, more local
type aliases instead. I also removed the explicit passing of template
parameters to functions since they were not needed. That, and I turned the
std::enable_if_t into static assertions that should give more
understandable error messages.

lorenzhs/ssssort