[bind10-dev] single vs multi module for libdns++ python binding

[zhanglikun]

 For comparison, dnspython uses multiple (sub)modules for "message",
> "name", "rrset", etc.  And, I felt it might be more convenient if we
> want to define module specific functions (which are not class
> methods).  It may also help separate the binding C++ source files per
> functionality (= python "module").  

+1