message: handle the error that occurs when getting the price of a name in a namespace that does not exist.
  Also, add a method to get a zonefile
diff: @@ -46,6 +46,10 @@ export class BlockstackNetwork {
  .then(resp => resp.json())
  .then(resp => resp.name_price)
  .then(namePrice => {
  + if (!namePrice) {
  + throw new Error(
  + `Failed to get price for ${fullyQualifiedName}. Does the namespace exist?`);
  + }
  let result = null
  if (namePrice.satoshis) {
  // backwards compatibility
  @@ -193,6 +197,17 @@ export class BlockstackNetwork {
  })
  }
  + getZoneFile(zonefileHash: string) {
  + return fetch(`${this.blockstackAPIUrl}/v1/zonefiles/${zonefileHash}`)
  + .then(resp => {
  + if (resp.status === 200) {
  + return resp.body.buffer().then((buf) => buf.toString)
  + } else {
  + throw new Error(`Bad response status: ${resp.status}`)
  + }
  + })
  + }
  +
  /**
  * Performs a POST request to the given URL
  * @param {String} endpoint the name of
  