Feature request: support for multiple velocypacks in vpack-to-json tool

[davechallis]

I'm trying to debug some output returned by the velocystream protocol, which consists of multiple velocypacks (header plus response body).

Parsing this with the vpack-to-json tool only decodes the first velocypack (i.e. the header), so it would be very handy if the tool could decode multiple concatenated velocypacks in some way.