Merge release 1.10.4 (all code by kristaps@), providing four new features:

Merge release 1.10.4 (all code by kristaps@), providing four new features:
1) Proper .Bk support: allow output line breaks at input line breaks,
but keep input lines together in the output, finally fixing
synopses like aucat(1), mail(1) and tmux(1).
2) Mostly finished -Tps (PostScript) output.
3) Implement -Thtml output for .Nm blocks and .Bk -words.
4) Allow iterative interpolation of user-defined roff(7) strings.
Also contains some minor bugfixes and some performance improvements.