[CM] Snd 20.7

[bil at ccrma.Stanford.EDU]

Snd 20.7:

Snd: new configuration switch: --with-notcurses; uses nrepl.

s7: added emscripten support for webassembly, thanks to Christos Vagias
     mingw fix thanks to Kjetil

checked: gtk 3.99.0|1, OSX 10.15.6, sbcl 2.0.8

Thanks!: Christos Vagias, Kjetil Matheussen