Update documentation to reflect https://pcgenorg.atlassian.net/browse/NEWTAG-477 , i.e. that the FEAT, VFEAT, AUTO:FEAT, ADD:FEAT, PREFEAT tags are now obsolete.
I've fixed all the immediate documentation of the FEAT tags.
Remaining work is to fix every place the FEAT tags are mentioned - they are used many, many times in the LST file tutorials. Personally, I think those tutorials are very stale and it would be better to re-write them and patch them up to current standards.