[Swan-dev] *cmp is a little harder to read

[D. Hugh Redelmeier]

I'm concerned about eb8a4265ffd98aa2f41a5b98c83876fcbfd19671
    timers: add more generic deltatime_cmp()
    
    expect use to follow the convention: deltatime_cmp(a, b) OP 0
    for instance deltatime_cmp(a, b) <= 0; like strcmp() et.al.

It is true that *cmp is a more general primative.  But it is also
harder to read code using it.

So: it is fine to add deltatime_cmp but I disagree with this comment:
+bool deltaless(deltatime_t a, deltatime_t b); /* obsolete; use deltatime_cmp() */

Uses of deltaless seem clearer to me than their replacement.