Votf with random value within range

[davelab6]

Building on the @dberlow "votf" proposal (for accessing OpenType Feature capabilities as design space locations, so that eg you can get pnum, tnum, onum, or smcp, from a set of axes locations instead of duplicated glyph data) I see a need from @ctrlcctrlv for making the location random within a specific range.

https://twitter.com/davelab6/status/1200443729825476609?s=19