[Doc]Update link to sliced scrolls doc (logstash-plugins#106)

* Update link path to sliced scrolls

* Added PR number to changelog link

Merge pull request logstash-plugins#104 from robbavey/fix_except

Remove Hash#except from failing spec.

bump to 4.3.0

set default_codec doc attribute

bump to 4.2.0

[skip ci] update gemspec summary

enable use of metadata fields in `add_field` decorations

By performing event decorations after the metadata field has been populated
we enable the supported `add_field` decoration to reference metadata fields.

Resolves logstash-plugins#76

Fixes logstash-plugins#78

Fix broken link

Fixes logstash-plugins#77

Version bump

For elastic/logstash#7993

[ci skip]

bump patch level for doc generation