Move events into their own module

The events were cluttering the `model` module, and so are now moved into
their own `model::event` module.

As users should not usually have to work with events all that much -
only currently in some rarely used event handlers - this change should
not be much more effort to import from.

i.e.:

```rs
use serenity::model::event::ChannelPinsAckEvent;
```
vs. the now-old:

```rs
use serenity::model::ChannelPinsAckEvent;
```

1 files changed, 4 insertions, 2 deletions

diff --git a/src/model/mod.rs b/src/model/mod.rs
index 5d1540b..832cda4 100644
--- a/src/model/mod.rs
+++ b/src/model/mod.rs
@@ -1,8 +1,10 @@
-pub mod permissions;
-
 #[macro_use]
 mod utils;
 
+pub mod event;
+pub mod permissions;
+
+
 mod channel;
 mod gateway;
 mod guild;