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, 3 insertions, 3 deletions

diff --git a/src/http/mod.rs b/src/http/mod.rs
index d79f7fd..5288f5c 100644
--- a/src/http/mod.rs
+++ b/src/http/mod.rs
@@ -39,7 +39,7 @@ use hyper::net::HttpsConnector;
 use hyper::{header, Error as HyperError, Result as HyperResult, Url};
 use hyper_native_tls::NativeTlsClient;
 use internal::prelude::*;
-use model::*;
+use model::prelude::*;
 use multipart::client::Multipart;
 use parking_lot::Mutex;
 use self::ratelimiting::Route;
@@ -524,7 +524,7 @@ pub fn delete_messages(channel_id: u64, map: &Value) -> Result<()> {
 ///
 /// ```rust,no_run
 /// use serenity::http;
-/// use serenity::model::{ChannelId, MessageId};
+/// use serenity::model::id::{ChannelId, MessageId};
 ///
 /// let channel_id = ChannelId(7);
 /// let message_id = MessageId(8);
@@ -1342,7 +1342,7 @@ pub fn get_guild_webhooks(guild_id: u64) -> Result<Vec<Webhook>> {
 ///
 /// ```rust,no_run
 /// use serenity::http::{GuildPagination, get_guilds};
-/// use serenity::model::GuildId;
+/// use serenity::model::id::GuildId;
 ///
 /// let guild_id = GuildId(81384788765712384);
 ///