[Request]: Support the rest of the EventSource public APIs

[rcampbel]

Request:

• As a Dev, I would like the ability to add event handlers for specific events dynamically after time of connection, so that I can have other events add event listeners based off a sse response.
• As a Dev, I would like the ability to remove event handlers for specific events dynamically after time of connection, so that I can have other events remove event listeners based off a sse response.
• As a Dev, I would like the ability to dispatch events for specific events dynamically, so that I can rebroadcast event after making changes to it a sse response.

Proposal:

• Update the method to better follow the the whatwg spec for EventSoruce response.

Reasoning:

• Allow for devs to dynamically attach and detach event handlers as needed.
• Follow standards put in place in spec while expanding functionality.