V2/parameter events

this is a patch that provides interfaces for listening to parameter changes.

it relies on https://github.com/oampo/Audiolet/pull/43 which is not merged into version-2 yet which makes this commit log kind of messy.

the relevant commits are:

1. [Adding EventEmitter and emitting parameter changes on AudioletNodes and AudioletParameters](https://github.com/catshirt/Audiolet/commit/e2714095954311598e8d465ea36f552812a93635)
2. [adding parameter event example](https://github.com/catshirt/Audiolet/commit/f8469b1081aa458ef323d05347ed8b79eae025a2)

the example and comments should hopefully explain the commit sufficiently.