Application Updates

[DakotaLarson]

Hi,
I have created a PR to pass along some (what I would consider) important updates to this package.

Current Issues:

• With the HTTP API, Auth headers are not passed reducing the quantity of requests I can make to unauthenticated endpoints by half.

• Additionally, upon inspection of the code, I found the use of setTimeout before a request is invoked. This will delay any request by 10ms minimum and doesn't always happen.

• I have still received 429s using this package. Therefore, I am unsure if the timeout functionality is working correctly, however, that is not addressed in this PR.

• With the WS API, it is a known issue that BitMEX will close websockets when many trades take place. There is no listener appended to the websocket to detect when the connection is closed.

Fixes:

• Always pass auth headers if they are present.
• Only use setTimeout if necessary
• Allow users to pass custom delay for ping
• Use more efficient refresh() method for ping timeout
• Allow users to pass callback listener for websocket close event

I tested the code, but didn't create any tests since none existed previously. I figure that falls outside the scope of this PR.