Drag&drop mod support (Patreon)

Full drag & drop mod support for Retroquad, including multiple mod folders at once.

When dragging multiple folders, the mod folder under the mouse cursor will be the main mod (i.e. you can define the order when dragging multiple mods).

Also, look how clean Retroquad's base folder is now. No DLLs, no batch files, no clutter.

Some other news:

• Improved the ordering of the lightning & horizon fading kernels, to make them smoother.
• Fixed the console background blending, now it uses the quadricolor blending maps properly.
• Fixed cvarlist corruption, and ordered all cvars & commands alphabetically. This affects what will show up when the console autocompletion is used.
• The debug build now compiles and works properly.
• Miscellaneous fixes and improvements under the hood.

This version will be available for all patrons this weekend. The menu system reengineering will require some significant work, so I'm not sure if it will be finished this month.