* Fix typo in Step 2
* Fix incorrect code referenced in Step 3, TODO 7. Update comments in
MathFunctions/CMakeLists.txt to unique strings.
* Resolve inconsistencies between steps in MathFunctions/CMakeLists.txt
* Updated output message
* Use 'target_compile_definitions' for HAVE_LOG and HAVE_EXP
Previously, the change from using TutorialConfig.h to
target_compile_definitions happened without explanation as part of Step 8.
Migrate tutorial text from individual `directions.txt` files to the main
tutorial document. Add some comments to source code to provide anchors
for inclusion.