The SocketioClient will be responsible for negotiating a web socket
connection and streaming results.

This should work for JSON responses as well as the only difference is
they come one at a time and do not have a length prefix.

This component is responsible for performing the handshake and returning an
initialized websocket connection.

Multiple threads can receive incoming message copies from the Websocket
connection. Also, multiple threads can safely call WriteMessage.

The namespace is responsible for translating between arbitrary
incoming messages for a given SocketIO endpoint and a specific iex message
type, such as TOPS. It is also responsible for forwarding the decoded
messages to all concerned listeners. Lastly, it filters out messages that
given listeners are not concerned with. All this allows multiplexing of
endpoint subscriptions over the same SocketIO connection.

Also simplifies encoding to handle only messages of known formats rather than
trying to handle arbitrary structs in a consistent manner.

Adds a subUnsubMsgFactory function type for generating subscribe and unsubscribe
messages for symbols across the given endpoint types.

PacketData contains the standard SocketIO info.

It turns out the connection can be initialized with two GET requests.

Also added an example demonstrating an IEX SocketIO negotiation and added
cookie support to the default client.

Replace the public API with callbacks.

Also, simplify the namespace by removing "Connections."

Messages from IEX uppercase symbol strings. Also add a quick example.

Because the DEEP endpoint only allows subscribing to one symbol at a
time, this allows all code paths to share the same logic rather than
special-casing DEEP.