Add 'patch' feature simliar to Kubertes' Kustomize

[birchb1024]

Kustomize has sed-like features which allow matching on a subtree (patch) or on maps with multiple keys, unlike Goyamp which currently matches on a single key. This enhancement would add rewrite logic in a similar way. Perhaps something like this:

define:
    $some-input:
         foo:
            alpha: 23
            bar:
               quux:
---
patch:
    - $some-input
    - foo:
         bar: 42

Outputs

foo:
  alpha: 23
  bar: 42