CMake Style Guide

[jdeaton]

This issue is a placeholder for my notes & work in progress for defining a style guide for our custom CMake modules and CMakeLists.txt files.

Some references:

• http://nupic.docs.numenta.org/1.0.2/contributing/cmake-style-guide.html
• http://docs.ros.org/jade/api/catkin/html/user_guide/standards.html
• https://community.kde.org/Policies/CMake_Coding_Style
• https://cmake.org/cmake/help/v3.13/manual/cmake-developer.7.html
• https://gist.github.com/mbinna/c61dbb39bca0e4fb7d1f73b0d66a4fd1
• https://github.com/richq/cmake-lint
• https://llvm.org/docs/CMakePrimer.html
• https://github.com/onqtam/awesome-cmake