The real CMake support

This patch provides a CMakeLists.txt file to build JSON-C library without relying on auto-tools support. This makes the build a bit more portable and cleaner.

It can detect headers and symbols and generate config.h header file based on those detections. It cannot yet handle ctest(1) as the testing itself depends on comparing the output against files. Testing would need some creative abuse of CMake :) This will be provided a few patches later and may possibly involve refactoring test cases.

The patch has been tested on GCC 4.8.5 (Linux), GCC 7.2.0 (MinGW) and Microsoft Visual C++ 16.0 (2010?) locally. Also, compiles correctly on Travis CI and AppVeyor without errors.

appveyor.yml

@@ -1,39 +1,37 @@
 version: '{branch}.{build}'
 os: Windows Server 2012 R2
 
-configuration:
-- Debug
-- Release
 platform: x64
+
+# There should be a better way to set-up a build matrix.
 environment:
   matrix:
-  - PlatformToolset: v140
-  - PlatformToolset: v120
-  - PlatformToolset: Windows7.1SDK
+    - b_toolset: Windows7.1SDK
+      b_config: Debug
+
+    - b_toolset: Windows7.1SDK
+      b_config: Release
+
+    - b_toolset: v120
+      b_config: Debug
+
+    - b_toolset: v120
+      b_config: Release
+
+    - b_toolset: v140
+      b_config: Debug
+
+    - b_toolset: v140
+      b_config: Release
 
 build_script:
-- cmake .
-- >
-  msbuild "json-c.vcxproj" /m /verbosity:normal
-  /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
-  /p:PlatformToolset=%PlatformToolset% /p:OutDir=lib\
+- cmake -T %b_toolset% -DCMAKE_BUILD_TYPE=%b_config% -DCMAKE_INSTALL_PREFIX=t_install .
+- cmake --build . --target install
 
 after_build:
-- md include\json-c
-- copy json.h include\json-c\*
-- copy debug.h include\json-c\*
-- copy linkhash.h include\json-c\*
-- copy arraylist.h include\json-c\*
-- copy json_util.h include\json-c\*
-- copy json_object.h include\json-c\*
-- copy json_tokener.h include\json-c\*
-- copy json_object_iterator.h include\json-c\*
-- copy json_c_version.h include\json-c\*
-- copy json_inttypes.h include\json-c\*
-- copy include\json_config.h include\json-c\*
-- copy json_object_private.h include\json-c\*
-- 7z a json-c.lib.zip lib\json-c.dll %Configuration%\json-c.lib %Configuration%\json-c.exp %Configuration%\json-c.pdb include\json-c\*.h
+- cd t_install
+- 7z a ../json-c.win32.%b_toolset%.%b_config%.zip *
 
 artifacts:
-- path: json-c.lib.zip
-  name: json-c.lib.zip
+- path: json-c.win32.%b_toolset%.%b_config%.zip
+  name: json-c.win32.%b_toolset%.%b_config%.zip