Add Move constructors

[lanzkron]

Add move constructors to Json::Value and Json::Value::CZString

As requested by issue #223: Json::Value should support move semantics

[BillyDonahue]

Please don't indent preprocessor directives. It's churning the diff.

[lanzkron]

Don't you think it makes the conditions much more readable?
I have no problem to adhere to the coding standards of the project if you think that's better

[BillyDonahue]

I don't think the indents as written improve the clarity of the file overall.

The usual thing is to keep the # in column 1. This is historical convention.
The next token is indented by 0, 1, or 2 spaces. In this project, it's 0, but you've chosen 8.

The idea is to keep the preprocessor lines visually segregated from the C++ code.
A reader can eyeball column 1 and see a run of #, which is easy.

[cdunn2001]

I rebased onto master (which is better than merging) your code as #267. Move discussion to there, or simply pull that branch and git push -f into your own fork to update this PR.

Don't worry about compatibility. We'll deal with that.

[lanzkron]

Rebased by @cdunn2001 in #267, closing this pull request

[cdunn2001]

I have a question: Why do we need to add the move ctor if the default version is provided automatically? ... Oh, I guess the rules for this have evolved. But could we use the new =default notation, instead of writing it ourselves?

[lanzkron]

Yeah, if you have a destructor or a copy constructor then the move
constructor will not be generated.

Even if this is not the case from a practical point of view I don't think
all compilers currently generate a default move constructor.

I think we could have done something like:

 Value(Value&&) = default;

But not all current compilers support this either :(

Note: I originally replied to your email which didn't contain the =default suggestion (for some reason) which is why my answer is phrased as it is.

[cdunn2001]

Oh, I sometimes update the comment for clarity. I guess that doesn't send a new e-mail.

Thanks, Motti.

[BillyDonahue]

The implicit move ops don't work for resource-managing classes like Json::Value::CZString.
It would just move (copy) the data members one by one. cstr_ and index_ are just pointer and int, so they'd be copied into the destination, but the source would not be changed and would still think of itself as the owner of its cstr_ data.

[lanzkron]

@BillyDonahue good point!