Make 'bind [KEY] "save quicksave.zds"' work on Linux and Mac OS(?)

[Premo36]

The workaround 'bind [KEY] "save quicksave.zds" (see #14 for details) does not work under Linux (and probably also under MacOS, can't test as I don't own a mac), as quicksave.zds gets saved in the home folder and not in the dml 2.x folder. Also the workaround as it is now will still not work as the gzdoom executable installed trough apt (located at /usr/games, which it's just a bash script that execute the real executable at /opt/gzdoom/gzdoom) does not have the "save" folder next to it as all user data is stored in ~/.config/gzdoom.

Could be fixed by using something like this is in the mono version, and warn the user in the readme that as been tested with only recent version of gzdoom/zandronum installed trough apt and that it may not work on older/portable version of those sourceports and that it's not tested under Mac OS:

string homePath = Environment.GetEnvironmentVariable("HOME")

string destinationPath = Path.Combine(homePath, ".config"); 
destinationPath = Path.Combine(destinationPath, executableName)

//Move any .zds file from the home folder to destinationPath

[Premo36]

Fixed for Linux system that use recent version of gzdoom installed trough apt (or similar). Should work also for Zandronum but is untested. Not fixed for Mac OS