Provide a way to configure Cores

[hstde]

At the moment the only way to chance core-variables is to hardcode them into core_environment() RETRO_ENVIRONMENT_GET_VARIABLE.
It would be much cleaner if you could provide a configuration file as a commandline argument where you can specify these parameters.

[navy1978]

if you download the version from my repo: https://github.com/navy1978/retrorun
you can configure retrorun settings and core settings via retrorun.cfg