Open files with existing Gvim window in Windows

from Vim Tip #1003:

`For example,

assoc .php=PHPFile
ftype PHPFile=“C:\Program Files\Vim\Vim63\gvim.exe” –remote “%1”

then whenever you double click a .php file in explorer, it will be opened in existing Gvim window (or it will open new Gvim window if there is no already opened Gvim window).`