appveyor.yml: Compile and test with latest version for __cplusplus ma…

According to [1] the C++ macro __cplusplus has always the value 199711L
even if you enable later version of C++ support via /std.

Use one job with /Zc:__cplusplus defined so that we know that it
compiles.

[1]: https://docs.microsoft.com/en-us/cpp/build/reference/zc-cplusplus?view=vs-2019

Rename argument array_index to array_indx in json_pointer methods

fix error 'setw' is not a member of 'std' in Wandbox example

Update LICENSE.MIT

PR for #2006 to test in AppVeyor.

Avoid mix-up with array_index member
Co-Authored-By: Niels Lohmann <niels.lohmann@gmail.com>

Update README.md : add a FAQ about memory release

Fix typo in examples

README: Fix string representation of `dump`ed `json`

Fixes gcc48 warning:

declaration of ‘array_index’ shadows a member of 'this' [-Wshadow]

As is it's confusing and inconsistent with the indented form right below. The backslash escapes make it confusing.

Some typos

Readme: Updated links to hunter repo & docs

Fix link to parse function in README

hunter was recently passed over to a new maintainer, this is why the github url & the link to the documentation have changed.

Adds instruction for using Build2's package manager

(proper naming suggested by `build2`'s author)

I created a `nlohmann-json` package for `build2` (https://build2.org) that have been published on the central public repository https://cppget.org : https://cppget.org/nlohmann-json (at the moment you can see that there is only one version: 3.7.3).

The repository of the package code is there: https://github.com/build2-packaging/nlohmann-json and is owned by the build2 community now. (with build2 you can use either a repository like cppget.org or a git repository so both are useful to users for different use cases).

This patch just add the basic information as to how to use this library with build2.

Update README.md

Fix warning: ignoring return value

docs: add central repository as conan source to readme