When changing data, you can only overwrite the top-level key/value

[mikrostew]

It would be nice to be able to add/change data at levels other than just the top level.

For example:

const yamlFM = require('yaml-fromat');

yamlFM.writeString(
`---
foo:
  bar: baz
  bam: boom
---

Some other things`,
`foo:
  bam: bam`
).then(console.log);

// ---
// foo:
//   bar: baz
//   bam: bam
// ---
//
// Some other things

Note: This will probably need an option to merge instead of overwrite