Resolve relative outputs with asset spec base dir
Resolve relative outputs with asset spec base dir

When the output is relative and the base directory is a static asset
the static view configuration will not be able to resolve the absolute
output path into a URL. To resolve it requires knowing the original
base directory setting, if it was an asset spec, so that the the call
to `static_url` can be passed an asset spec of the output.

sontek/pyramid_webassets