skipping all uses of a type

[sweirich]

It would be convenient to be able to say

skip type Outputable.SDoc

and have it skip all functions that use that type.

This would replace individual skips of functions throughout the development, such as these from module-edits/SrcLoc/edits.

pprUserRealSpan
pprUserSpan

I don't think it should skip type definitions that depend that type. I think we'll need ad hoc solutions for those cases. (Either skipping those types too, or redefining them so that they don't mention the skipped type.)