refactor parallel stub arrays into behavior objects (#244)
move async method generation to stub behavior (#244)
add onCall to stubs for building sequences (#244)
allow onCall to be combined with returns* and throwsException in stub behavior sequences (#244)
move callback sequence tests in onCall section (#244)
allow overriding asnyc stub behavior with sync behavior (#244)
fix paretheses of parseInt call
make fakes delegate to parent stub behvior (#244)

* store a reference back to the parent stub on a fake
* if a fake neither has a behavior for the current call index nor a
  default bahavior, delegate to the parent
* as a result calling resetBehavior on a fake makes it fall back to
  its parent behavior again
delegate withArgs on behavior back to stub (#244)

* pass callIndex to behavior
* delegate withArgs back to stub invoking matching onCall
invoking onCall alone should not alter stub behavior (#244)

otherwise delegation of onFirstCall().withArgs(...) to
withArgs(...).onFirstCall() creates a blank behavior for first
call. Calls not matching the specified args do not fall back to
default stub behavior then.
extract behavior to own file (#244)