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, 5 insertions, 5 deletions

diff --git a/src/builder/edit_guild.rs b/src/builder/edit_guild.rs
index 45969fe..b15658c 100644
--- a/src/builder/edit_guild.rs
+++ b/src/builder/edit_guild.rs
@@ -1,5 +1,5 @@
 use internal::prelude::*;
-use model::{ChannelId, Region, UserId, VerificationLevel};
+use model::prelude::*;
 use std::collections::HashMap;
 
 /// A builder to optionally edit certain fields of a [`Guild`]. This is meant
@@ -56,7 +56,7 @@ impl EditGuild {
     /// from the cwd and encode it in base64 to send to Discord.
     ///
     /// ```rust,no_run
-    /// # use serenity::model::GuildId;
+    /// # use serenity::model::id::GuildId;
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
@@ -112,12 +112,12 @@ impl EditGuild {
     /// Setting the region to [`Region::UsWest`]:
     ///
     /// ```rust,no_run
-    /// # use serenity::model::GuildId;
+    /// # use serenity::model::id::GuildId;
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
     /// #     let mut guild = GuildId(0).get()?;
-    /// use serenity::model::Region;
+    /// use serenity::model::guild::Region;
     ///
     /// // assuming a `guild` has already been bound
     ///
@@ -163,7 +163,7 @@ impl EditGuild {
     /// Setting the verification level to [`High`][`VerificationLevel::High`]:
     ///
     /// ```rust,ignore
-    /// use serenity::model::VerificationLevel;
+    /// use serenity::model::guild::VerificationLevel;
     ///
     /// // assuming a `guild` has already been bound
     ///