lib/authors.js
function gitAuthors (cb) {
  return exec('git log --pretty="%an <%ae>"', function (er, stdout, stderr) {
    if (er || stderr) throw new Error(er || stderr)
    return cb(null, stdout.split('\n').reverse())
  })
}
function gitAuthors (cb) {
  return exec('git log --pretty="%an <%ae>"', function (er, stdout, stderr) {
    if (er || stderr) throw new Error(er || stderr)
    return cb(null, stdout.split('\n').reverse())
  })
}
returns array of strings like "firstname lastname <email@host.com>" - first contributions are first in the list - contains duplicates - might not have a real email - might not have real name