`std::iterator` is deprecated

[adamnovak]

In C++17, inheriting from std::iterator is deprecated, on the theory that code is actually better if it just explicitly defines all the typedefs that std::iterator would get you by inheritance.

But it is still used e.g. here:

BBHash/BooPHF.h

Line 45 in 1803c23

class bfile_iterator : public std::iterator<std::forward_iterator_tag, basetype>{

This leads to compiler warnings when compiling under C++17 or later.