Update the resources category

[makorendev]

I made the following changes to the Resources category:

• Add Aseprite to Game Development Tools, under Graphics Editors. It feels odd not having a pixel art focused program here, aside from the passing mention of using Paint.NET for it.
• Add LDtk to Game Development Tools, under Map Editors. LDtk is a very Haxe friendly editor with HaxeFlixel integration, so it makes sense.
• Fix the inconsistent headings. Map Editors and Asset Utilities had bigger headings than the other two sections.
• Add a section to Using Haxelib about using libraries in your project after you install them.
• Fix the dead link in Using Haxelib.

[Geokureli]

thanks!