pass `isCurrent` argument only to `onAny` subscribers

also pass no arguments to `onEnd` subscribers
simplify code
pass single argument to .onAny subscribers i.e. event object
implement .combine using .sampledBy
minor changes in utils.js
delete accidentally added file
fix bug in .combine
fix bug in .flatMap
docs
automatically preserve isCurent in .withHandler
0.2.3
Merge branch 'master' into gh-pages

* master:
  0.2.3
  automatically preserve isCurent in .withHandler
  docs
  fix bug in .flatMap
  fix bug in .combine
  delete accidentally added file
  minor changes in utils.js
  implement .combine using .sampledBy
  pass single argument to .onAny subscribers i.e. event object
  simplify code
  pass `isCurrent` argument only to `onAny` subscribers