Add support for key nesting

[pogiedoge]

To avoid redundancy in values, I'd like to have the option to refer to the value of a different object nested in one object's value. The nesting should work by prefixing the desired key.

Take the following example:
`
{
"red": "red",
"apple": "apple"
"red_apple": "$red $apple"
}

Output:
red
apple
red apple
`

In this example, the $ character serves as the prefix for the nested key, but the feature should be able to handle any string configured by the user as a prefix.