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;
```

0 files changed, 0 insertions, 0 deletions