Break up the model module

The `model` module has historically been one giant module re-exporting
all of the model types, which is somewhere around 100 types. This can be
a lot to look at for a new user and somewhat overwhelming, especially
with a large number of fine-grained imports from the module.

The module is now neatly split up into submodules, mostly like it has
been internally since the early versions of the library. The submodules
are:

- application
- channel
- error
- event
- gateway
- guild
- id
- invite
- misc
- permissions
- prelude
- user
- voice
- webhook

Each submodule contains types that are "owned" by the module. For
example, the `guild` submodule contains, but not limited to, Emoji,
AuditLogsEntry, Role, and Member. `channel` contains, but not limited
to, Attachment, Embed, Message, and Reaction.

Upgrade path:

Instead of glob importing the models via `use serenity::model::*;`,
instead glob import via the prelude:

```rust
use serenity::model::prelude::*;
```

Instead of importing from the root model module:

```rust
use serenity::model::{Guild, Message, OnlineStatus, Role, User};
```

instead import from the submodules like so:

```rust
use serenity::model::channel::Message;
use serenity::model::guild::{Guild, Role};
use serenity::model::user::{OnlineStatus, User};
```

1 files changed, 6 insertions, 5 deletions

diff --git a/src/framework/standard/configuration.rs b/src/framework/standard/configuration.rs
index 23148e3..d54a821 100644
--- a/src/framework/standard/configuration.rs
+++ b/src/framework/standard/configuration.rs
@@ -1,6 +1,7 @@
 use client::Context;
 use http;
-use model::{GuildId, Message, UserId};
+use model::channel::Message;
+use model::id::{GuildId, UserId};
 use std::collections::HashSet;
 use std::default::Default;
 use super::command::PrefixCheck;
@@ -101,7 +102,7 @@ impl Configuration {
     /// #
     /// # impl EventHandler for Handler {}
     /// # let mut client = Client::new("token", Handler).unwrap();
-    /// use serenity::model::GuildId;
+    /// use serenity::model::id::GuildId;
     /// use serenity::framework::StandardFramework;
     ///
     /// client.with_framework(StandardFramework::new().configure(|c| c
@@ -126,7 +127,7 @@ impl Configuration {
     /// #
     /// # impl EventHandler for Handler {}
     /// # let mut client = Client::new("token", Handler).unwrap();
-    /// use serenity::model::UserId;
+    /// use serenity::model::id::UserId;
     /// use serenity::framework::StandardFramework;
     ///
     /// client.with_framework(StandardFramework::new().configure(|c| c
@@ -287,7 +288,7 @@ impl Configuration {
     /// #
     /// # impl EventHandler for Handler {}
     /// # let mut client = Client::new("token", Handler).unwrap();
-    /// use serenity::model::UserId;
+    /// use serenity::model::id::UserId;
     /// use serenity::framework::StandardFramework;
     ///
     /// client.with_framework(StandardFramework::new().configure(|c| c
@@ -302,7 +303,7 @@ impl Configuration {
     /// #
     /// # impl EventHandler for Handler {}
     /// # let mut client = Client::new("token", Handler).unwrap();
-    /// use serenity::model::UserId;
+    /// use serenity::model::id::UserId;
     /// use std::collections::HashSet;
     /// use serenity::framework::StandardFramework;
     ///