3.0.0

• Allow providing listener id manually via a third argument in .on() and .once() methods.
• Add 4 different modes to Emitter to handle duplicate listener ids.
• Add possibility to throw on duplicate listeners in Emitter.
• Improve unit tests (migrate from Ava to Mocha + Chai).
• Improve documentation.
• Remove UniqueEmitter (since Emitter can now do the same thing).
• Remove experiments.
• Update dev dependencies.