dbg: remove dbg and add log system
warnings--
model: use stream operator to perform io

efyj::dexi use operator<< and operator>> to perform read and write
operation. So, global functions in io.hpp and io.hpp removed. io.cpp is
renamed into model-io.cpp
utils: merge print activity with utils

The stringf function merged with utils header.
log: add missing EFYJ_API for log class
warning--