Lua CJSON Module

CJSON parser with the following modifications:

• Loads the cjson module in a global cjson table
• The encode buffer is limited to the sandbox output_limit.
• The decode buffer will be roughly limited to one half of the sandbox memory_limit.
• The NULL value is not decoded to cjson.null it is simply discarded. If the original behavior is desired use cjson.decode_null(true) to enable NULL decoding.
• The new() function has been disabled so only a single cjson parser can be created.
• The encode_keep_buffer() function has been disabled (the buffer is always reused).