The book is available for purchase and download from Leanpub.com
LeanPub allows us to update the book frequently. This means that after purchase you can download the most recent version of the book whenever you need it.
If you decide to move to a different book reader, you can download the version required for that reader at no additional cost. LeanPub books have no DRM. This means that you can copy and read the book on any device you choose to.