async function get (url, key, opts) {
  await setupPromise
  var origin = opts && opts.dontExtractOrigin ? url : await extractOrigin(url)
  if (!origin) return null
  if (opts && opts.normalizeUrl) origin = normalizeUrl(origin)
  return cbPromise(cb => {
    db.get(`SELECT value FROM sitedata WHERE origin = ? AND key = ?`, [origin, key], (err, res) => {
      if (err) return cb(err)
      cb(null, res && res.value)
    })
  })
}
@param {string} url
@param {string} key
@param {Object} [opts]
@param {boolean} [opts.dontExtractOrigin]
@param {boolean} [opts.normalizeUrl]
@returns {Promise<string>}