Feature request: passthrough body property

[ryanblock]

The existing data property is a nice way to pass in an object of structured params to POST, etc.

It'd be great to have a body property that just passes straight through. So with tiny I could in theory do the following:

// JSON encoded
await tiny.post({
  url,
  data: { whatev: true }
})

// Form URL encoded
await tiny.post({ 
  url,
  headers: { 'content-type': 'application/x-www-form-urlencoded' },
  body: 'whatev=true'
})