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

[cppalliance-bot]

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

[cppalliance-bot]

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

[cppalliance-bot]

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.70%. Comparing base (c02d872) to head (220ea73).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1070   +/-   ##
========================================
  Coverage    93.70%   93.70%           
========================================
  Files           91       91           
  Lines         9139     9139           
========================================
  Hits          8564     8564           
  Misses         575      575           

Files with missing lines	Coverage Δ
include/boost/json/detail/value_to.hpp	100.00% <100.00%> (ø)

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1070/pullrequest.html

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1070/pullrequest.html

[grisumbras]

I have an idea for an alternative approach. I'll implement it first, so that I can compare yours with mine.

[grisumbras]

My alternative: #1075.