Snd 20.9:

Snd: clm.rb and snd-test.rb updated for Ruby 3.0, thanks to Mike.

s7: add s7_load_c_string and s7_load_c_string_with_environment
    tools/tmock.scm, tnum.scm, concordance.scm
    notcurses_s7.c assumes version 2 of notcurses; for version 1, pass -DNOTCURSES_1=1.

checked: Fedora 33, Ubuntu 20.10, sbcl 2.0.10

Thanks!:  Woody Douglass, Christos Vagias, Mike Scholz, IOhannes m zmoelnig, 
          David Runge
