Remove cruft from Logger class

A big code simplification and cruft removing, make
Logger class a singleton and fully self conteined.
Also add direction indicators (">>" and "<<") to
better differentiate input and output lines in the
log file.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/misc.h

@@ -60,6 +60,6 @@ private:
   sys_time_t t;
 };
 
-extern void logger_set(bool b);
+extern void start_logger(bool b);
 
 #endif // !defined(MISC_H_INCLUDED)