Feature Request: extract JSON pointer from SingleIssue #84

Currently, the result of validate is a SingleIssue with a "julian" path representation, such as for example [foo][1][bar], stored in issue.path.

I would like to extract the JSON pointer in its standardized format, that is to say #/foo/0/bar in this case. It is difficult to get there for 2 reasons:

1. One needs to figure out whether to convert [a][1] to #/a/0 (if 1 was an integer index of an array) or #/a/1 (if 1 was the string "1" as an object key).
2. Things get messy if I have a "a]" key or something like that in my JSON object.

My suggestion would be to store the path as a path::Vector{Union{Int, String}} and only build the string when displaying the issue. From the path it would be straightforward to generate a JSON pointer. Ideally, there could be a public method to get a json_pointer(issue::SingleIssue).