Fix spelling
Hard require 5.010

It can't really do much with 5.8 and lower, really
Tidied grandfathered features
Support attaching additional features
postderef implies postderef_qq
Add autoderef to grandfathered list

This feature is available on 5.14+, but gives an experimental warning on
5.19.8+.
Made additional-pragma logic recursive
Made 'switch' include 'smartmatch'
v0.006

          Hard require 5.010
          Support attaching additional features
          Add autoderef to grandfathered list for 5.14-5.18