Some examples are missing from build

[pdhahn]

When I build OCCA with examples enabled (via cmake) I get some but not all. In particular, I do not get cpp/15_finite_difference and cpp/16_mandelbulb.

Since it is not clear how to explicitly enable specific examples in the OCCA cmake setup, I presume there is some sort of hidden cmake logic involved in determining which examples to build. I am not proficient in cmake so I cannot confirm this by examining CMakeLists.txt etc.. In any case:

1. I would like to know how to enable these missing examples for build (if possible).
2. I request that the OCCA development team extend the cmake configuration to allow selection of specific examples to include or exclude from the build (presumably when in the cmake-gui, the "Advanced" option is enabled).

Thanks!