Added a readme. Also added a rad.Response struct.

The rad.Response struct will most likely be returned via a response
channel. This channel will be returned to the callee on initializing
a downloader.
Download blob and new function
Renamed a bunch of things. More explanaions to follow.
Added a Fetch method to DownloadBlob, added StartWorkers to start
workers. Fixed the init function.

1) DownloadBlob has a Fetch method that takes a string and returns a
rad.Response. DownloadBlob implements DownloadWorker.

2) StartWorkers takes a slice of DownloadWorkers. It runs each
DownloadWorker's Fetch method in a goroutine. The goroutine listens for
url strings on one channel and returns responses on another channel.

3) The init function will create 10 workers. The 10 workers can be used
through the Fetch and Reply channels.