PlEncoding headers for frequent Pl-objects

[mgondan]

This seems to be on cpp's todo list. Would you please check if I am on the right path? Then I will add a few unit tests and make a few cosmetic changes.

[kamahen]

Please also add test cases for the new methods/functions.

(I'm travelling right now, so I might take a few days to respond)

[mgondan]

Would you please check if I am on the right path?

I take your responses as a yes :-)

[kamahen]

it's probably a good idea to do one function or constructor change all the way through (including a test case) to confirm that the compiler is happy with it (I've been fooled before).

[mgondan]

Added constructors and "compiler" tests such as PlAtom atom(3, "äöü", PlEncoding::UTF8), i.e., just the declarations, no tests so far.

Happy to hear your feedback. I will continue thereafter.

[kamahen]

If you don't have a test that uses a constructor (or function), then the compiler won't do all the semantic checks because it won't generate any code.

BTW, one of my earlier comments was wrong -- you shouldn't make any changes to SWI-cpp2-plx.h unless there has been a change to SWI-Prolog.h.

[mgondan]

If you don't have a test that uses a constructor (or function), then the compiler won't do all the semantic checks because it won't generate any code.

I added a more unit tests, the PR is now ready for review.