Zipit Z2 Expanded Bottom Case

This is a larger bottom case for the [Zipit Z2](https://mozzwald.com/zipitz2) handheld computer. It's main purpose is so that you can add a larger battery as the original battery or equivalent replacement is not readily available. This is the second version which fixed a few errors in [the first](https://mozzwald.com/articles/2016/07/03/expanded-zipit-bottom-case-my-first-3d-printing-adventure).