Collect unknown keywords as annotations

[karenetheridge]

see json-schema-org/json-schema-spec#987 -- this is a specifiation "SHOULD" for draft 2020-XX but we can implement it sooner.

Add an option to disable this behaviour, but it should default to true.

Also adjust the behaviour of the format keyword accordingly.

[karenetheridge]

version 0.020 adds this as an option, defaulting to false.

[karenetheridge]

done.