Add file.getBuffer() API

[feross]

New convenience API:

file.getBuffer(function callback (err, url) {})

Get the file contents as a Buffer.

The file will be fetched from the network with highest priority, and callback will be
called once the file is ready. callback must be specified, and will be called with a an
Error (or null) and the file contents as a Buffer.

file.getBuffer(function (err, buffer) {
  if (err) throw err
  console.log(buffer) // <Buffer 00 98 00 01 01 00 00 00 50 ae 07 04 01 00 00 00 0a 00 00 00 00 00 00 00 78 ae 07 04 01 00 00 00 05 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>
})

[feross]

Released as 0.21.0.