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/structures/PermissionOverwrites.js

@@ -1,4 +1,5 @@
 const Permissions = require('../util/Permissions');
+const Util = require('../util/Util');
 
 /**
  * Represents a permission overwrite for a role or member in a guild channel.
@@ -59,6 +60,10 @@ class PermissionOverwrites {
       .delete({ reason })
       .then(() => this);
   }
+
+  toJSON() {
+    return Util.flatten(this);
+  }
 }
 
 module.exports = PermissionOverwrites;