Add configuration file evaluation

[sdilts]

In Stumpwm, users are able to have initialization code ran at startup so they can customize the WM's behavior. We need the same thing in Mahogany.

Requirements for a complete implementation:

• config files should follow the XDG base directory specification
• There should be a command line flag to startup Mahogany without this file.
• Enabling / disabling evaluation could be a compile time option.
• Errors during evaluation should not cause Mahogany to crash or shutdown.

Like with defcommand, not all of this needs to be implemented at once.

[Arian-D]

Regarding the first requirement, would an implementation similar to StumpWM's load-rc be okay?

[sdilts]

Ya, that should work for now. I'd like to get rid of the old-school .stumpwmrc and .stumpwm.d style configuration locations, or at the very least not have them be prioritized over anything in the XDG conf directory.

My main concern would be error handling. I guess I'd try to eval the file before starting the rendering loop, and just crash if there's an error?

[Arian-D]

Perfect! Also, I just saw this PR which seems to be addressing this, so I'll follow the progress there.

[tpine]

@Arian-D I haven't had the time to finish completing all the issues brought up in the PR review and Im not sure when I will so Im happy for you to take over from where that pr is at the moment if you want. I think from memory I have fixed the accidental indentation of code around it and removing the format calls.

[Arian-D]

Thanks @tpine!

I'll try to have a look this weekend, and will see how to go about it.