Support event emitters from PaymentsSDK and Resource

[perrin4869]

Closes #38

This works by using the newListener and removeListener events - whenever the Resource or PaymentsSDK gets an event handler, it is relayed to the underlying api object.
However, eventemitter3 doesn't support these built-in events, so it had to be replaced with a more straightforward node polyfill. The good thing here is that in node environments, we'll just keep using the regular node module. The bad news is that standard node typings are not as strict as the eventemitter3 typings - these do not support generics, so the events are not type safe anymore.

[coveralls]

Coverage increased (+0.02%) to 96.41% when pulling 0d54a61 on feature/perrin4869/sdk-resources-ee into b08fe01 on master.

[phieronymus]

Nice trick 🙂 Would it be possible to add the event it can listen to in the Readme? As the type disappeared I am scared that finding what the logging is capable of will be harder to find.

[perrin4869]

Done!

[phieronymus]

Thanks a lot! Merging this 🙂