After grabbing the latest 0.13-release to sync up with Boost 1.67, I ran into a big issue in my debug build.
I constantly hit an assert in the checked iterators so had to track it down and fix it.
The current code casts iterators from the partial_parsed buffer (which can be quite large) to iterators for the small temporary std::array buffer. MS implemented their checked iterators using the statically-declared size of the array (which is much smaller than partial_parsed) so they hit all the time.

Also, that static_cast likely only worked because compilers likely use char* as the iterator type for both containers, but I don't think assuming that is portable.

I changed chunk_encoding_parser so that its operator() and update_chunk_size can take any compatible iterator_range type as arguments.