Support of key option for yaml including alias

[k2tzumi]

If yaml includes alias, encrypt it with the key option specified.

bundle exec yaml_vault encrypt plain.yml -o encrypted.yml -k 'foo'

• plain.yml

  foo: &foo
  x: 1
  y: 2
  bar:
  <<: *foo
  z: 3

https://github.com/joker1007/yaml_vault/blob/2e37a160c0cf8dc584c870beff7f0e1c9ef4bffc/lib/yaml_vault.rb#L24

In order to encrypt the specific key or less after expansion, places that don't want to be plain have been expanded. (Foo.x, foo.y are encrypted but bar.x, bar.y are not encrypted)

• encrypted.yml(As-is)

  foo:
  x: encrypted-1
  y: encrypted-2
  bar:
  x: 1
  y: 2
  z: 3

• encrypted.yml(expect)

  foo: &foo
  x: encrypted-1
  y: encrypted-2
  bar:
  <<: *foo
  z: 3

  Or

foo:
  x: encrypted-1
  y: encrypted-2
bar:
  x: encrypted-1
  y: encrypted-2
  z: 3

[joker1007]

Thanks! I understand this case. But it is difficult. This feature needs Psyck low level interface and YAML AST Processing. I don't have enough time to implement it for now.