Configurable Odroid XU4 Open-Frame Case

This provides a user-configurable open-frame case for use with the Hardkernel/Odroid XU4 ARM processor board.

This is a highly modified adaptation of version 1e of the XU4 case openSCAD script originally provided by user hominoid on the Hardkernel/Odroid support forum at www.forum.odroid.com. See the original 'Split Air Flow Vertical or Horizontal Case' thread at URL https://forum.odroid.com/viewtopic.php?f=97&t=26373

Four fundamental case configurations are supported in this adaptation:
- no case fan (sampleA in the files)
- fan mount on case top plate (sampleB in the files)
- fan mount is on "outside" of a case end (sampleC in the files)
- fan mount is on "inside" of fan on a case end (sampleD in the files)

The inside mount and outside mount configurations provide "split airflow" cooling of the XU4, with some airflow passing both below and above the XU4. The outside fan mount configuration is the original hominoid design. Various minor aspects of the case ar