Change EventType to an interface with a type argument

[Arcath]

Brief Description

Change EventType to an interface with a type argument so that the data attribute can be typed implicitly. For example, once you set the event type to EventType<EVENT_ATTACK> the data takes on the type EventData[EVENT_ATTACK]. This also lets the type of data be addressable so you can write functions that expect a certain type of event data.

This also fixes #109 as EventType incorrectly used type instead of event.

Checklists

• Test passed
• Coding style (indentation, etc)
• Edits have been made to src/ files not index.d.ts
• Run npm run dtslint to update index.d.ts

[Arcath]

I've updated the type to something that better describes the return data, it's either null or an object that might have these properties.

The index type is only there so typescript will let you address it as EventData[X] which is how the EventItem type works.

[Meekohi]

Awesome :D