again so as not to break old SVG-Edit which fail at *presence* of
`namespace` (fixes#274)
- Known regression: Remove Openclipart as its site's now setting of
`X-Frame-Options` to `"sameorigin"` makes it unusable on our end
for our cross-origin uses
- Forward compatibility enhancement: For IAN image library, add
`svgedit=3` param to URL so that it can keep using old API for
SVG-Edit versions before 3, while conditionally using new object-based
API now (and if we switch exclusively to the object-based API in the
future, this site will continue to work)
- Docs: Add "Forward compatibility enhancement" to list
Brett Zamir