Feature request: cleanupIDs -- preserve IDs matching regex

[tremby]

It'd be useful to preserve particular IDs by regex, in such cases where the exact IDs to preserve aren't necessarily known until build time, or where it'd be a pain to maintain a long list.

For example, preserve IDs matching /^svgshape_/.

I might provide a pull request for this if there is interest.

[bdrtsky]

I was surprised this feature doesn't exist yet. I don't see any other way to remove that damned Layer_2 wrapper g tag...