Added new "span" mode

Use color management protocol and load images with glycin

Add `--layer` option for customizing the layer name / layer namespace

man: -m default to stretch

Support to explicitly set layer shell namespace

Use color management protocol on suitable PNG images

Set opaque regions on `create_layer_surface`

Render SVG files at output resolution

Update compiled version string to include swaybg version when Git is used

Fix crash when new output added