Windows Azure Storage driver

Implement storage driver for Windows Azure Blob Storage.

Some helpful links:

http://msdn.microsoft.com/en-us/library/ee924681.aspx
http://msdn.microsoft.com/en-us/library/dd179355.aspx
http://msdn.microsoft.com/en-us/library/dd179376.aspx

Have finished implementation. Working on test cases now. Will submit it for review soon.
The driver supports the following

• Azure Block Blobs support (default)
• Azure Page Blobs (ex_page_type option)
• Support for leasing blobs while being updated (ex_use_lease option)

Review for this ticket: https://github.com/apache/libcloud/pull/91