Add toJSON methods (#1859)

* tojson things

* fix client

* ignore private properties

* remove extra property descriptors

* handle primitive flattening

* remove unused import

* add toJSON to collections

* reduce stateful props

* state

* allow custom prop names when flattening

* fix client

* fix build

* fix flatten docs

* remove guild.available, cleanup permissions, remove arbitrary id reduction

* fix util import

* add valueOf as needed, update member props

* fix incorrect merge

* update permissionoverwrites and permissions

remove serialization of permissions in PermissionOverwrites#toJSON.
change Permissions#toJSON to serialize permissions, by default excluding
admin checks.

* change Permissions#toJSON to return the primitive

* Permissions#toJSON explicitly return bitfield

src/util/Permissions.js

@@ -102,6 +102,10 @@ class Permissions {
     return Object.keys(this.constructor.FLAGS).filter(perm => this.has(perm, checkAdmin));
   }
 
+  toJSON() {
+    return this.bitfield;
+  }
+
   valueOf() {
     return this.bitfield;
   }