v0.3.12

- Support WebAssembly

- Implement batch rendering
- Implement WASM font rendering via HTMLCanvasElement
- Implement SDL_ttf font rendering for SDL backend
- Use GL_DEPTH_COMPONENT16 on WASM builds
- Rename texcoord_offset to texcoord_pixel
- Pin external library versions
- Add Image and Texture comparison operators
- Add Painter::set_debug / debug singleton API
- Pin position attribute to location 0 on macOS
- Simplify Painter_draw_image to fill-only
- Add libsdl2-ttf-dev to CI apt packages
- Remove deprecated has_rdoc= from gemspecs