1) Breaking change: g3 namespace replaces g2
2) g2log.hpp remains in src/g2log.hpp... but now all it does is to include the g3log.hpp, etc
3) ALL HEADER FILES ARE IN src/g3log/ while all .cpp and .ipp files are in /src (exception for g2log.hpp)
This should make it EASIER for clients to copy/install the header files to the new location. It greatly simplifies
rpm and cpackage installationsw