I had to wrap LinearTransform.operator() in afw.
Otherwise it was straightforward.
However, I am not very happy with astrometry_net.cc. It has a lot of C++ code mixed in with the usual pybind11 wrapper. The extra code is there as a shim to astrometry_net's C code, so it's reasonable to have there, but the file feels cluttered to me. Suggestions for cleanup welcome.
Note that we will be moving our wrapper of astrometry_net into a new package at some point (soon after we switch to pybind11, I hope, but so far other things have always taken priority). So if a very invasive sort of cleanup is wanted, it might be best to defer that until the split.