Restructure the client to be a command line client.

The client used to be a sample code to demonstrate how to use Genomics
API with Go. This patch starts migrating that into a full command line
client, similar to the Java client.

Supported commands in this change:

  reads search
  readsets get
  readsets search
Merge pull request #3 from namn/master

Restructure the client to be a command line client.