code: public static Observable<String> from(final Reader reader, final int size) {
          return Observable.create(new OnSubscribeReader(reader, size));
      }
docs: Reads characters from a source {@link Reader} and outputs {@link Observable} of
  {@link String}s. Supports backpressure.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/St.from.png" alt="">
  
  @param i
  Source {@link Reader}
  @param size
  internal buffer size
  @return the Observable of Strings read from the source