Thanks for the parser, surprisingly easy to use!
I found I wanted some extra stuff, like unescaping strings and converting jsmntype_t into text. I wrote some stuff (it's in a Git repo on another project - cf. issue #47) and with tests, so I could convert back to .hg and make a pull request.
Do you want extras, given they could be completely omitted and not increase the footprint if there were unwanted?
What about additions that add a (void*) to jsmn_parser and some extra code to jsmn.c, for generating errors?