Yaml overlay

this has come up again for me, is their an easy way to overlay yaml documents?

ex-

···

---
  a:
    i: 1
    ii: two
  b:
    - 1
    - 2
  ---
  a:
    ii: 2
    iii: 3
  b:
    - 3

overlayed becomes:

  ---
  a:
    i: 1
    ii: 2
    iii: 3
  b:
    - 1
    - 2
    - 3

Basically the overlay rules are 1) append collecitons 2) replace scalars

Thanks
--
T.