The CustomSerializer class was made final, so the CustomReferencedNormalizer
class must be updated to use composition over inheritance

* 'master' of github.com:bistrosk/elasticsearch-dsl:
  Update README.md

update readme

fix empty objects being normalized as arrays

update to PHP 8 & ES 8

# Conflicts:
#	composer.json

# Conflicts:
#	composer.json

* bump development version number

* missing support

added missing support to [field value factor](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html#function-field-value-factor)

* updated docs

* proposed changes