Using data dir based on freedesktop specs

[andy5995]

Instead of using ~/.vs-fltk, it might be worth considering checking for $XDG_DATA_HOME first, and if that doesn't exist, use ~/.local/share/vs-fltk

XDG Base Directory Specification

[KaruroChori]

I am not too convinced about this one.
There are many applications following the freedesktop specs... and many more which do not.

For example, on the laptop I am writing from, bun, cargo, dillo, mozilla, npm, platformio, renpy, wine, thunderbird, vscode-oss, they are all located in home within their folder. They don't split their files between .config and .local/share, they keep all user related data in one place.

Only flatpak, gambas3, godot, nano & Mousepad follow this convention.

So, even if it is a standardization effort, its adoption is somewhat limited from what I can tell and it would require me to split user's file in multiple places.