Add more Swagger API docs

[andrewmarklloyd]

• Add docs for the error route. See conversation in Add swagger doc #70 for more information
• The eventData maps to a specific eventType's required keys. For example the playEpisode eventType eventData has 3 fields: episodeName, minutesPlayed, and minutesRemaining. I would add an example, like:

example: {
    episodeName: "Ethereum Governance with Hudson Jameson",
    minutesPlayed: 1622.53,
    minutesRemaining: 117.62
}