Document JSON API implementation defs and progress in class

Author: bf4

CHANGELOG.md

@@ -32,6 +32,7 @@ Fixes:
 - [#1488](https://github.com/rails-api/active_model_serializers/pull/1488) Require ActiveSupport's string inflections (@nate00)
 
 Misc:
+- [#1482](https://github.com/rails-api/active_model_serializers/pull/1482) Document JSON API implementation defs and progress in class. (@bf4)
 - [#1551](https://github.com/rails-api/active_model_serializers/pull/1551) Added codebeat badge (@korzonek)
 - [#1527](https://github.com/rails-api/active_model_serializers/pull/1527) Refactor fragment cache class. (@groyoh)
 - [#1560](https://github.com/rails-api/active_model_serializers/pull/1560) Update rubocop and address its warnings. (@bf4 @groyoh)

lib/active_model_serializers/adapter.rb

@@ -84,10 +84,11 @@ def find_by_name(adapter_name)
     end
 
     # Gotta be at the bottom to use the code above it :(
-    require 'active_model_serializers/adapter/base'
-    require 'active_model_serializers/adapter/null'
-    require 'active_model_serializers/adapter/attributes'
-    require 'active_model_serializers/adapter/json'
-    require 'active_model_serializers/adapter/json_api'
+    extend ActiveSupport::Autoload
+    autoload :Base
+    autoload :Null
+    autoload :Attributes
+    autoload :Json
+    autoload :JsonApi
   end
 end