Add macros for logging and debugging

[iboukhss]

We now have these macros inspired by glog

LOG(DEBUG);
LOG(INFO);
LOG(WARN);
LOG(ERROR);
LOG(FATAL);

They can be used just like std::cout

Example:

LOG(DEBUG) << "Server started";

This flowchart can also be helpful

I picked the blue color for DEBUG messages.

Closes #11