Tutorial: Improve Step 1

* Update minimum required version to 3.10
* Use VERSION argument to project command rather than separate variables
* Replace `endif(USE_MYMATH)` with  more modern `endif()`
* Simplify the call to 'configure_file()'
* Add comments to tutorial.cxx to use as anchors in documentation
* Remove CMakeLists and TutorialConfig.h.in files that users should
  create. Consequently, remove Step1 from CMake tests.

Help/guide/tutorial/Step10/tutorial.cxx

@@ -16,7 +16,8 @@ int main(int argc, char* argv[])
     return 1;
   }
 
-  double inputValue = std::stod(argv[1]);
+  // convert input to double
+  const double inputValue = std::stod(argv[1]);
 
   const double outputValue = mathfunctions::sqrt(inputValue);