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, 10 insertions, 1 deletions

diff --git a/src/model/utils.rs b/src/model/utils.rs
index 52e3bbc..9d4ca88 100644
--- a/src/model/utils.rs
+++ b/src/model/utils.rs
@@ -2,7 +2,7 @@ use parking_lot::RwLock;
 use serde::de::Error as DeError;
 use std::collections::HashMap;
 use std::sync::Arc;
-use super::*;
+use super::prelude::*;
 
 #[cfg(feature = "cache")]
 use internal::prelude::*;
@@ -12,6 +12,10 @@ use super::permissions::Permissions;
 #[cfg(all(feature = "cache", feature = "model"))]
 use CACHE;
 
+pub fn default_true() -> bool {
+    true
+}
+
 pub fn deserialize_emojis<'de, D: Deserializer<'de>>(
     deserializer: D)
     -> StdResult<HashMap<EmojiId, Emoji>, D::Error> {
@@ -112,6 +116,11 @@ pub fn deserialize_single_recipient<'de, D: Deserializer<'de>>(
     Ok(Arc::new(RwLock::new(user)))
 }
 
+pub fn deserialize_sync_user<'de, D>(deserializer: D)
+    -> StdResult<Arc<RwLock<User>>, D::Error> where D: Deserializer<'de> {
+    Ok(Arc::new(RwLock::new(User::deserialize(deserializer)?)))
+}
+
 pub fn deserialize_users<'de, D: Deserializer<'de>>(
     deserializer: D)
     -> StdResult<HashMap<UserId, Arc<RwLock<User>>>, D::Error> {