Update C++ tutorial and very simple C++ program

[ischoegl]

The very simple C++ program should be updated to use newSolution.

More importantly, no longer having setup_cantera scripts (see Cantera/enhancements#135) may require some additional steps (example: PKG_CONFIG_PATH needs to be set)

[speth]

That example gives an explicit compiler command demonstrating the use of the -L and -I flags to point to the Cantera library and header file locations, and as such does not rely on setup_cantera or pkg-config at all. Assuming that command line is modified correctly for the user's system, I think it should work fine, with the caveats that are already mentioned in the example, e.g. that the set of libraries to link to depends on how Cantera was built.

[ischoegl]

Now that I have things working, I can add the following about the Compiling C++ Programs tutorial:

• The PKG_CONFIG_PATH requires the pkgconfig folder to be specified, e.g. PKG_CONFIG_PATH=/path/to/lib/pkgconfig
• In a conda environment, setting of environment variables further needs conda env config vars set PKG_CONFIG_PATH=/path/to/lib/pkgconfig
• LD_LIBRARY_PATH needs to be set
• The SConstruct example needs fmt and yaml-cpp added to the LIBS list

In the past, PKG_CONFIG_PATH and LD_LIBRARY_PATH were set/updated by setup_cantera, so I think there is a link to Cantera/enhancements#135