Add fast json module

[waruqi]

We need provides JSON support for xmake/lua.

Need Features

• Fast and Small
• Only uses c or lua
• Full support for JSON with UTF-8
• No dependencies on other libraries

Some Options

• tbox/object (json)
• https://github.com/openresty/lua-cjson/
• https://github.com/mpx/lua-cjson
• http://dkolf.de/src/dkjson-lua.fsl/home (dkjson)
• https://github.com/brimworks/lua-yajl
• https://github.com/jiyinyiyong/json-lua
• https://github.com/grafi-tt/lunajson
• https://github.com/rxi/json.lua

Some performance tests

• https://www.kyne.com.au/~mark/software/lua-json-performance.html

[waruqi]

Maybe https://github.com/openresty/lua-cjson/ is a good option.

[waruqi]

#894

[waruqi]

我看cjson封的接口挺好的，目前就先直接将cjson原样导出到 core.base.json下了，回头有需求再改进。