JSON Flattener

{
  "user.name.first": "John",
  "user.name.last": "Doe",
  "user.age": 30,
  "user.address.street": "123 Main St",
  "user.address.city": "New York",
  "user.hobbies[0]": "reading",
  "user.hobbies[1]": "coding"
}