suggestion: support flat paths only

[dominictarr]

The best argument with depject is that the paths are easily greppable.

if you have this

{foo: {bar: true, baz: true}}

it's not easy to grep this file to see it contains foo.baz = true
but if it's this format:

nest({
  'foo.bar': true,
  'foo.baz': true
})

then it's easy. The other things you can do with this module is just confusing, but with this example, it's pretty clear what the syntax does.