Fix typos in locks in ws_string

Fixes accidental double-unlocks in several ws_string methods.
Merge pull request #290 from xVin/fix-ws_string-locks

Fix typos in locks in ws_string
Add deserializer callback interface
Add deserializer callback source file (stubs) and CMakeLists.txt entry
Add implementation for NULL callback
Add implementation for boolean callback
Add implementation for integer callback
Add implementation for string callback
Add implementation for start_map callback
Fix: Name of a command must be assignable.
Add implementation of map_key callback
Add implementation of end_map callback
Add implementation of start_array callback
Add implementation of end_array callback
Set callback table
Add key for stack position argument type
Add state for stack position argument type state
Allow subdirectories for serializer tests
Remove main serialize testing file, we want to split the tests
Add CMakeLists.txt file for json deserializer tests