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/ReactionEmoji.js

@@ -1,3 +1,4 @@
+const Util = require('../util/Util');
 const Emoji = require('./Emoji');
 
 /**
@@ -15,6 +16,14 @@ class ReactionEmoji extends Emoji {
      */
     this.reaction = reaction;
   }
+
+  toJSON() {
+    return Util.flatten(this, { identifier: true });
+  }
+
+  valueOf() {
+    return this.id;
+  }
 }
 
 module.exports = ReactionEmoji;