feature: ENV-Variable support would be awesome

[typoworx-de]

I'm rarely searching for a node-yaml parser that can handle env-variables and variable-substitutes:

myvar: bar

config:
   foo1: ${bar}
   foo2: ${env: MY_GLOBAL_VAR}

Demo:
MY_GLOBAL_VAR=Hello node .

resulting in:

{
    myvar: "bar"
    config: {
        foo1: "bar"
        foo2: "Hello"
    }
}