Update C++ tutorial

[ischoegl]

• Replace newPhase by newSolution in C++ examples
• Add information on environment variables to C++ compilation tutorial

Closes #191

[ischoegl]

@speth ... ended up replacing newPhase in the remaining tutorials also, and fixed a couple of other things that were not up-to-date in the documentation. I tested compilation of all examples, and things work as expected.

[ischoegl]

Fwiw, some of the includes can be simplified if Cantera/cantera#1238 were to be adopted.

[bryanwweber]

As @speth mentioned elsewhere, I don't think now is a good time to get into a conversation about the content of the include files. I'd prefer not dropping the lowercase include files from the examples.

I think we should limit this PR to the changes in the export and library configuration, and defer changing the examples until later. Since the website can be updated independently of a release, we can change these to newSolution later.

[ischoegl]

@bryanwweber ... thank you for the comments.

As @speth mentioned elsewhere, I don't think now is a good time to get into a conversation about the content of the include files. I'd prefer not dropping the lowercase include files from the examples.

I'm totally fine with keeping 'convenience' headers. At the same time, not having Solution.h covered is not great.

I think we should limit this PR to the changes in the export and library configuration, and defer changing the examples until later. Since the website can be updated independently of a release, we can change these to newSolution later.

I'm not sure I agree here: newSolution pretty much replaced most of the instances in the C++ test suite already, and is overall much more convenient for the users to use (see factory_demo.cpp!).

My preferred solution would be to switch the imports to

#include "cantera/core.h"

as proposed in PR Cantera/cantera#1238 (will wait on feedback there).

PS: If Cantera/cantera#1238 goes ahead, I'd redirect this PR to testing.

[ischoegl]

@bryanwweber and @speth ... now that cantera/core.h is deferred (PR Cantera/cantera#1238), I updated the examples so they are up to date for the 2.6 release (and also work for 2.5.1). This is ready for another round of reviews.

[speth]

Thanks, @ischoegl. This looks good to me.