Documentation improvements (#2069)

* docs: fix documentation in various places

All stores: resolveID returns a nullable Snowflake
GuildAuditLogs: ActionType also can be ALL
MessageEmbed: make files property show up in the docs
ClientApplication: resetSecret and resetToken return a promise
ClientManager: status is readonly
Guild: features is an array of strings and ban no longer accepts a number or string
Guild: ban method no longer accepts a string or number
GuildMember: ^
RichPresenceAssets: small and large Image are Snowflakes, also fixed parameter documentation for small and large image url method
WebhookMessageOptions: file property is no longer a thing

* docs: improve GuildAuditLogs documentation

Prefix types with AuditLog to avoid confusion
Document GuildAuditLogs' static Targets and Actions properties and add necessary typedefs
Use typdefs over primitives where possible.

* fix documentation for Guild#defaultRole

src/stores/GuildMemberStore.js

@@ -41,7 +41,7 @@ class GuildMemberStore extends DataStore {
   /**
    * Resolves a GuildMemberResolvable to an member ID string.
    * @param {GuildMemberResolvable} member The user that is part of the guild
-   * @returns {?string}
+   * @returns {?Snowflake}
    */
   resolveID(member) {
     const memberResolveable = super.resolveID(member);