Rewrite CMake tutorial
Rewrite CMake tutorial

Rewrite the CMake tutorial, splitting it into functional sections which
are hopefully easier to digest, and updating it for the new helper
functions introduced a couple commits back.

lcm-proj/lcm,lcm-proj/lcm,lcm-proj/lcm,adeschamps/lcm,adeschamps/lcm,bluesquall/lcm,bluesquall/lcm,lcm-proj/lcm,adeschamps/lcm,lcm-proj/lcm,bluesquall/lcm,adeschamps/lcm,lcm-proj/lcm,adeschamps/lcm,lcm-proj/lcm,adeschamps/lcm,bluesquall/lcm,bluesquall/lcm,bluesquall/lcm,bluesquall/lcm,lcm-proj/lcm,adeschamps/lcm,adeschamps/lcm