Refactoring iterators: Not derived from std::iterator any more.
Refactoring iterators: Not derived from std::iterator any more.

Deriving from std::iterator seems to be deprecated these days. Instead just
define the types ourselves. For discussion see
http://stackoverflow.com/questions/6471019/can-should-i-inherit-from-stl-iterator

mapbox/pbf.hpp,mapbox/pbf.hpp,mapbox/pbf.hpp