refactor(BitField): base class for Permissions, ActivityFlags, Speaking (#2765)

* abstract BitField from Permissions

* reduce useless code, improve docs

* add a ReadOnly identifier to the return type of Bitfield#freeze()

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-1.html#partial-readonly-record-and-pick

* fix the RangeError

* update docs, convert Speaking and ActivityFlags to bitfields

* fix some docs

* Fix Speaking BitField oops

* docs for oops

* more incorrect docs

* Fix incorrectly named property

* add new classes to index

* fix missing @extends docs

* default bitfield resolve to 0, and cleanup defaulting everywhere

Also removes GuildMember#missiongPermissions() alias that had incorrect behavior

* Breaking: Rename Overwrite allowed and denied to allow and deny

To be consistent with the api's naming

* fix setSpeaking usage to bitfields instead of booleans

* fix speaking bug in playChunk

* docs: Updated typings

* fix: BitFieldResolvable should use RecursiveArray

* bugfix/requested change

* typings: Cleanup (#2)

* typings: Fix BitField#{toArray,@@iterator} output type

* typings: correct PermissionOverwrites property names and nitpicks

src/util/Speaking.js

@@ -0,0 +1,22 @@
+const BitField = require('./BitField');
+
+/**
+ * Data structure that makes it easy to interact with a {@link VoiceConnection#speaking}
+ * and {@link guildMemberSpeaking} event bitfields.
+ * @extends {BitField}
+ */
+class Speaking extends BitField {}
+
+/**
+ * Numeric speaking flags. All available properties:
+ * * `SPEAKING`
+ * * `SOUNDSHARE`
+ * @type {Object}
+ * @see {@link https://discordapp.com/developers/docs/topics/voice-connections#speaking}
+ */
+Speaking.FLAGS = {
+  SPEAKING: 1 << 0,
+  SOUNDSHARE: 1 << 1,
+};
+
+module.exports = Speaking;