stdlib: Fix maps:from_list/1 spec.
stdlib: Document Maps module
erl_docgen: Generate map() instead of #{} for maps type
Merge branch 'egil/maps/doc-module-api'

* egil/maps/doc-module-api:
  erl_docgen: Generate map() instead of #{} for maps type
  stdlib: Document Maps module
  stdlib: Fix maps:from_list/1 spec.