Added get_tags() support for subscriptions. (#26)

* Added get_tags() support for subscriptions.

* missed a parameter

* Update DESCRIPTION

* Update DESCRIPTION

R/az_subscription.R

@@ -26,6 +26,7 @@
 #' - `list_role_assignments()`: Lists role assignments.
 #' - `get_role_definition(id)`: Retrieves an existing role definition.
 #' - `list_role_definitions()` Lists role definitions.
+#' - `get_tags()` Get the tags on this subscription.
 #'
 #' @section Details:
 #' Generally, the easiest way to create a subscription object is via the `get_subscription` or `list_subscriptions` methods of the [az_rm] class. To create a subscription object in isolation, call the `new()` method and supply an Oauth 2.0 token of class [AzureToken], along with the ID of the subscription.
@@ -85,6 +86,7 @@ public=list(
     state=NULL,
     policies=NULL,
     authorization_source=NULL,
+    tags=NULL,
     token=NULL,
 
     initialize=function(token, id=NULL, parms=list())
@@ -102,6 +104,7 @@ public=list(
         self$state <- parms$state
         self$policies <- parms$subscriptionPolicies
         self$authorization_source <- parms$authorizationSource
+        self$tags <- parms$tags
         NULL
     },
 
@@ -155,6 +158,13 @@ public=list(
             else sapply(apis, select_version)
         }
     },
+
+    get_tags=function()
+    {
+        if(is.null(self$tags))
+            named_list()
+        else self$tags
+    },
 
     get_resource_group=function(name)
     {