anchor.diff:  ;; ==> on-end
   ----
   
  +
   === Zip
   
   This combinator combines two observable sequences in one.
  
positive.code: This is implemented using protocols for make it flexible and easy extensible
  by the user. This is how the default impl behaves:
  
  - `js/Error` or `ExceptionInfo` instances triggers the error termination of stream.
  - `(rx/end value)` sends the unwrapped value to the stream, then terminate stream.
  - `rx/end` as value triggers the stream termination.
  - any other value are valid values for send to the stream.
  
  
  == Consuming streams
  
negative.code: (def sub (rx/on-end sub #(println "end!")))
  ----
  
  
  === Consume error termination
  
  With `on-error` function you can watch the error termination of an observable
  