Support for using find method with json pointers

[Smakson]

Currently, one can use json pointer to check for whether a path is present in a json object via contains and one can access the path via at and operator[]. However, this effectively forces us to do the sequence of lookups along the path twice which forces the user that wants to use JSON pointer into an unnecessary performance pessimization.

From looking at the existing implementations of e.g. contains in the json_pointer class it seems like that would not be hard, in fact I am working on a branch/PR to propose an implementation, but I wanted to check here first what others think and whether this is intentionally left out as a feature.