Here are some fixes for webassets 0.8 as well as some other improvements.
I haven't tested yet with webassets 0.7 to be sure it still works. I will do so and report back, but wanted to give you an early peek.
add globbing to resolver
avoid recreating the AssetResolver over and over
remove unreachable code
handle relative output paths
support asset specs for inputs on webassets 0.8