feat: cleanup

[antouhou]

This PR:

Adds:

• A method to render to a softbuffer surface via render_to_argb32 that accepts a mutable slice of u32 - the format that is supported by the softbuffer;
• A method to render to a Vec - render_to_buffer;

Removes:

• Text rendering - moved to protextinator crate;
• Old image rendering methods - now you can use textures and texture layers instead;

Changes:

• Vertex format: fill color is now per-instance, not per-vertex - reduces memory usage