Speed up Windows Appveyor tests

[cxw42]

The Windows build of #199 ran out of time --- https://ci.appveyor.com/project/xuhdev/editorconfig-vim/builds/45234274/job/c2ncdng2dyya2d0n

Edit write a little C program to do the arg parsing and invoke vim, instead of using chained bat/ps1? Lots of options linked to here. Maybe choco MSYS2, then use glib's g_shell_parse_argv() from an MSYS2 program?

Edit Or just use the Linux editorconfig wrapper via msys2 bash?