Fix union header
Add method for initialisation of a ws_value_union from a value
Force enumeration value for invalid values to be 0
Merge pull request #243 from neithernut/add-values-union_features

Add union features
Add common header for yajl backend
Add common.c for yajl JSON backend including stubs
Add allocation function callbacks including stubs
Add allocation func table
Add implementation for serializer_yajl_state_new()
Add implementation of serializer_yajl_state_free()
Add JSON deserializer backend interface definition
Add deserializer file with stubs
Add yajl callbacks definitions and stubs
Add YAJL callback table
Add implementation for ws_serializer_json_deserializer_new()
Add deserialize callback with stub
Pass deserializer as context around
Pass size to yajl state object allocation

This way, the yajl state object becomes an abstract one
Add deserializer state type including allocator helper
Add start_map callback implementation