Event sending

I've tried to keep this as simple as possible.

Leaving BLYEvent.h as an optional import.

Class method to set the credentials, then just call trigger on the event.

``` objective-c
#import <Bully/BLYEvent.h>

[BLYEvent setAppID:@1 key:@"app_key" secret:@"app_secret"];
[[BLYEvent eventWithName:@"my_awesome_event_name" channels:@[@"the_cool_channel"] data:@{@"foo": @"bar"}] trigger];
```