JSON statistics

I have recently started using gdnsd for an internal project and was curious to know if it had JSON reporting. Upon searching I came across this post in Google Groups: https://groups.google.com/forum/?fromgroups=#!topic/gdnsd/hozZMjpiEWQ

So I figured I would add it to the current code base.

I admit that it has been a long time since I wrote any C code of note, but this was rather academic.