Gem

Clone of git://git.code.sf.net/p/pd-gem/gem 374f71368f4a54e8d0f7887460a178e9020a1ba4 w/bugfix to compile on windows/msys2. Should use https://github.com/umlaeute/Gem.git but v0.93 has build problems on Linux and HEAD crashes with [gemwin] on Linux