Improve cached's name and documentation (#594)

src/client/dispatch.rs

@@ -478,7 +478,7 @@ fn handle_event<H: EventHandler + Send + Sync + 'static>(
                     let event_handler = Arc::clone(event_handler);
 
                     threadpool.execute(move || {
-                        event_handler.cached(context, guild_amount);
+                        event_handler.cache_ready(context, guild_amount);
                     });
                 }
             }

src/client/event_handler.rs

@@ -10,11 +10,16 @@ use crate::client::bridge::gateway::event::*;
 
 /// The core trait for handling events by serenity.
 pub trait EventHandler {
-    /// Dispatched when the cache gets full.
+    /// Dispatched when the cache has received and inserted all data from
+    /// guilds.
+    ///
+    /// This process happens upon starting your bot and should be fairly quick.
+    /// However, cache actions performed prior this event may fail as the data
+    /// could be not inserted yet.
     ///
     /// Provides the cached guilds' ids.
     #[cfg(feature = "cache")]
-    fn cached(&self, _ctx: Context, _guilds: Vec<GuildId>) {}
+    fn cache_ready(&self, _ctx: Context, _guilds: Vec<GuildId>) {}
 
     /// Dispatched when a channel is created.
     ///