Add initial prototype.

3-mid/physics/implement/box2d/contrib/extern/sajson/CMakeLists.txt

@@ -0,0 +1,10 @@
+add_library(sajson STATIC sajson.cpp sajson.h)
+target_include_directories(sajson PUBLIC ..)
+
+set_target_properties(sajson PROPERTIES
+	CXX_STANDARD 11
+    CXX_STANDARD_REQUIRED YES
+    CXX_EXTENSIONS NO
+)
+
+source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} FILES sajson.cpp sajson.h)

3-mid/physics/implement/box2d/contrib/extern/sajson/sajson.cpp

@@ -0,0 +1,2 @@
+// This cpp is here to force cmake to make a project file for sajson.
+int sajson_dummy;