Boost Intrusive to be able to print the json pointer of where an error occourred when performing the value_to operation.

[RoyBellingan]

When used with

https://github.com/RoyBellingan/boostIntrusive/tree/master

It should produce this

------
default msg : source composite size does not match target size
expanded msg: the key >> timestamp << is non optional and missing in path /0/comment/0

------
default msg : source composite size does not match target size
expanded msg: the key >> author << is non optional and missing in path /0/comment/0/likes/1

------
default msg : not a number
expanded msg: Last json pointer was /0/comment/0/timestamp

[cppalliance-bot]

An automated preview of the documentation is available at https://1070.json.prtest2.cppalliance.org/libs/json/doc/html/index.html