I finally started adding config files for system options.

Notably, there are now config options for:

• screen resolution
• fullscreen (note: command-line fullscreen option removed)
• music volume
• keybindings

The keybindings.txt file provided with Flare is for QWERTY (notably the WASD movement).  If someone creates a QWERTZ, AZERTY, etc. version of this file I'll include it in the project.

Note that keybindings don't currently change the action bar display.  E.g. if you change "I" for Inventory to "B" for Backpack, the menu still shows a tiny "I" over the inventory icon.

As a side effect of this change, I read in config/settings.txt before anything else and I now gracefully quit the program if I can't open that file (e.g. if permissions are incorrect or if the executable is run in the incorrect working directory).