Tidy up the converter selection a bit; Move doc endpoints

I wasn’t sure why all the doc endpoints start '/csv'. I think that first /csv is for declaring the input format, in which case it shouldn’t be part of the doc urls for the operators, because they won’t be affected by the choice of input format.

It’s very possible I have misunderstood what that first '/csv' is about! This is a bit of a speculative pull request.