Resolve issues #4 and #6 and minor changes

- Resolve issues #4 and #6 as discussed in working session.
- The on, once, and off methods are no longer labeled as events (they are methods for attaching event handlers, not actually events.)
- A clarification remark is added to the "rejected" event, as it is currently the only event associated with the end of a call where the "disconnected" event is not also triggered.
- Call.addStream is edited to allow either orca.ManagedStream or RTCMediaStream as input, since the description notes that an RTCMediaStream can be passed in place of an orca.ManagedStream to be converted implicitly.

Comment: It is recommended to format the event string documentation more cleanly, as currently compiling the jsdoc results in a large unformatted block of text, since the whitespace present in the js file is lost.