Support map users and roles to multiple groups (#424)

* Support map users and roles to multiple groups

* Simplify code by rename `user_arn` to `userarn`, `role_arn` to `rolearn`

* Next version should be 6.x because PR this is a breaking change.

* Update example variables.tf

* Change indent to 2

* Fix map-aws-auth.yaml maybe invalid yaml.

CHANGELOG.md

@@ -7,7 +7,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Next release
 
-## [[v5.?.?](https://github.com/terraform-aws-modules/terraform-aws-eks/compare/v5.1.0...HEAD)] - 2019-08-??]
+## [[v6.?.?](https://github.com/terraform-aws-modules/terraform-aws-eks/compare/v5.1.0...HEAD)] - 2019-08-??]
 
 ### Added
 
@@ -19,6 +19,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+ - Support map users and roles to multiple groups (by @nauxliu)
  - Fixed errors sometimes happening during destroy due to usage of coalesce() in local.tf (by @petrikero)
  - Write your awesome change here (by @you)