Change signature of newCharReader to return uniqu_ptr

[AssafPassalCG]

Description
The current implementation of Json::CharReaderBuilder.newCharReader(), allocates memory, while there is no one to release it,
this issue causes a leak because when we upgraded to the new version, we didn't understand we should wrap the pointer with std::unique_ptr

Solution
Make the function return std::unique_ptr

Context
I opened that PR: #1420, and that closed because it is a breaking change. While I see the point of that, I actually think that if it will break someone's code, there is a good chance that it will save him from a memory leak.

[BillyDonahue]

We can't change the signature of this old and fundamental function.

We have a lot of user code written for that raw pointer return type, and changing it would require a change to nearly all programs that use the jsoncpp library. It's not IMO a problem requiring such a drastic change. C++ programmers are assumed to take care with raw pointers and avoid memory leaks, and ideally install leak detectors on their CI builds.

What we should do, however, is provide a similar but different function that returns a std::unique_ptr<CharReader>, and encourage transition to that one. Maybe makeCharReader? newCharReader can be discouraged and deprecated down the road but we do not need to remove it.

[AssafPassalCG]

I will create the PR, soon I hope

[AssafPassalCG]

Not sure how to mark the deprecated function

[AssafPassalCG]

#1424

[AssafPassalCG]

I finished the PR changes you requested, and most of the changes happened because I used reformat.sh script from the repo, maybe it a good idea to put some note that you shouldn't commit those changes