Fix typo in README

Update the README to better explain this, and make a few other tweaks.

Update the docs to mark all members of those structures deprecated, and
 suggest what to use instead.

Newer appveyor config for VS2022 etc...
Update the appveyor config to specify "image" instead of just "os", and build for VS2017, VS2019 and VS2022.

Fix/static include dirs

Really use prefix JSON_C_OBJECT_ADD_

This change introduces JSON_C_OBJECT_ADD_CONSTANT_KEY
as a replacement of JSON_C_OBJECT_KEY_IS_CONSTANT.

The description of json_object_object_add_ex tells to
look at the flags JSON_C_OBJECT_ADD_* but it is not
for JSON_C_OBJECT_KEY_IS_CONSTANT.

From the point of vue of a developper using json-c,
the function json_object_object_add_ex is mainly used,
not the hash facility, it seems more natural to provide
a regular naming of prefix JSON_C_OBJECT_ADD_CONSTANT_KEY.

* don't assume includedir

This change syncs the public header include install location with what gets written into pkgconfig file.

fix cmake version for tests

Fix use-after-free in json_tokener_new_ex()

The failure path taken in the event of printbuf_new() returning NULL
calls free() on tok->stack after already having freed tok. Swap the
order of the two calls to fix an obvious memory access violation.

Fixes: bcb6d7d347 ("Handle allocation failure in json_tokener_new_ex")
Signed-off-by: Juuso Alasuutari <juuso.alasuutari@gmail.com>

CMake create uninstall target if unix generator is used

Add AfterCaseLabel to .clang-format

This is to fix the behavior that might've changed between older versions of clang-format, I'm not sure.
Version 10 tries to put the bracket on the same line as case without this.

Check __STDC_VERSION__ is defined before checking its value

Prevent an undef warning regarding __STDC_VERSION__ by checking whether it is defined before checking its value.

To avoid target exe file export JSON functions.

[RFC] json_pointer: allow the feature to be disabled

Some users may not want to included it in their build/system. So allow a
cmake symbol to disable it.

A user can do 'cmake -DDISABLE_JSON_POINTER=ON <json_c_root_dir>' and
disable the json_pointer functionality. That saves about 17 KB (on an
x86_64) machine. This may be useful on smaller embedded systems; even
though the saving would be fewer kilobytes.

One thing that also needs to change a bit, is that the 'json.h' be
autogenerated via cmake, in order to conditionally include that
"json_pointer.h" file.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

The intent is to be able to disable some features that get built into the
library. When we do that, we also need to disable some tests.

It's easier when adjusting a variable that contains the list of test names,
versus modifying the list in the foreach() statement.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Fix unused variable for Win32 build in random_seed.c

fix invalid unsigned arithmetic.

random_seed: on error, continue to next method