Add deserializer callback interface
Add deserializer callback source file (stubs) and CMakeLists.txt entry
Add implementation of NULL callback
Add implementation of boolean callback
Add implementation of integer callback
Add implementation of string callback
Add implementation of start_map callback
Add implementation of map_key callback
Add implementation of end_map callback
Add implementation of start_array callback
Add implementation of end_array callback
Add static helper for setting up a transaction in the buffer
Set callback table
Add key for stack position argument type
Add state for stack position argument type state
Initial json deserializer testing setup
Add test for init/deinit deserializer
Add minimal test (empty string)
Add minimal json object test
Add tests for { "": <null,bool,int,string> }