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, 84 insertions, 0 deletions

diff --git a/src/model/application.rs b/src/model/application.rs
new file mode 100644
index 0000000..dca8e41
--- /dev/null
+++ b/src/model/application.rs
@@ -0,0 +1,84 @@
+//! Models about OAuth2 applications.
+
+use super::id::UserId;
+use super::user::User;
+use super::utils::default_true;
+
+/// Information about a user's application. An application does not necessarily
+/// have an associated bot user.
+#[derive(Clone, Debug, Deserialize)]
+pub struct ApplicationInfo {
+    /// The bot user associated with the application. See [`BotApplication`] for
+    /// more information.
+    ///
+    /// [`BotApplication`]: struct.BotApplication.html
+    pub bot: Option<BotApplication>,
+    /// Indicator of whether the bot is public.
+    ///
+    /// If a bot is public, anyone may invite it to their [`Guild`]. While a bot
+    /// is private, only the owner may add it to a guild.
+    ///
+    /// [`Guild`]: struct.Guild.html
+    #[serde(default = "default_true")]
+    pub bot_public: bool,
+    /// Indicator of whether the bot requires an OAuth2 code grant.
+    pub bot_require_code_grant: bool,
+    /// A description of the application, assigned by the application owner.
+    pub description: String,
+    /// A set of bitflags assigned to the application, which represent gated
+    /// feature flags that have been enabled for the application.
+    pub flags: Option<u64>,
+    /// A hash pointing to the application's icon.
+    ///
+    /// This is not necessarily equivalent to the bot user's avatar.
+    pub icon: Option<String>,
+    /// The unique numeric Id of the application.
+    pub id: UserId,
+    /// The name assigned to the application by the application owner.
+    pub name: String,
+    /// A list of redirect URIs assigned to the application.
+    pub redirect_uris: Vec<String>,
+    /// A list of RPC Origins assigned to the application.
+    pub rpc_origins: Vec<String>,
+    /// The given secret to the application.
+    ///
+    /// This is not equivalent to the application's bot user's token.
+    pub secret: String,
+}
+
+/// Information about an application with an application's bot user.
+#[derive(Clone, Debug, Deserialize)]
+pub struct BotApplication {
+    /// The unique Id of the bot user.
+    pub id: UserId,
+    /// A hash of the avatar, if one is assigned.
+    ///
+    /// Can be used to generate a full URL to the avatar.
+    pub avatar: Option<String>,
+    /// Indicator of whether it is a bot.
+    #[serde(default)]
+    pub bot: bool,
+    /// The discriminator assigned to the bot user.
+    ///
+    /// While discriminators are not unique, the `username#discriminator` pair
+    /// is.
+    pub discriminator: u16,
+    /// The bot user's username.
+    pub name: String,
+    /// The token used to authenticate as the bot user.
+    ///
+    /// **Note**: Keep this information private, as untrusted sources can use it
+    /// to perform any action with a bot user.
+    pub token: String,
+}
+
+/// Information about the current application and its owner.
+#[derive(Clone, Debug, Deserialize)]
+pub struct CurrentApplicationInfo {
+    pub description: String,
+    pub icon: Option<String>,
+    pub id: UserId,
+    pub name: String,
+    pub owner: User,
+    #[serde(default)] pub rpc_origins: Vec<String>,
+}