[doc] Add doc on real-time logger.

This version is more human readable.

doc/additionalDoc/doc-debug-real-time-logger.h

+/**
+\page subp_debug_rt_logger Real-time Logger
+
+ \section real_time_logger_quick_intro Quick introduction
+ Each entity has a protected logger_ object.
+ The simplest way to have information while running your graph is to initialize
+ it in the constructor, and then display information in the methods.
+
+ You can then change the level of information you want to display using
+ either the entity method setLoggerVerbosityLevel()
+ or the corresponding python bindings.
+
+ \section real_time_logger_modifying_entities Putting information in your entity.
+
+ It is possible to define the periodicity of the logger:
+ \code
+ logger_.setTimeSample(0.001); 
+ \endcode
+
+ To define the periodicity at which one wants to print information:
+ \code
+ logger_.setStreamPrintPeriod(0.005);
+ \endcode
+
+ Several level of verbosity are possible:
+ \code
+ logger_.setVerbosity(VERBOSITY_ALL);
+ \endcode
+ The full list of options are:
+<ul>
+<li>VERBOSITY_ALL: Accept all messages</li>
+<li>VERBOSITY_INFO_WARNING_ERROR: Accept messages at minimum level : INFO,
+WARNING, ERROR</li> <li>VERBOSITY_WARNING_ERROR: Accept messages at minimum
+level : WARNING, ERROR</li> <li>VERBOSITY_ERROR: Accept messages at minimum
+level : ERROR</li>
+</ul>
+
+It is specified by the enum LoggerVerbosity
+ 
+ It is possible to display information according to various level of debug:
+ \code
+ sendMsg("This is a message of level MSG_TYPE_DEBUG", MSG_TYPE_DEBUG);
+ \endcode
+ or
+ \code
+ DYNAMIC_GRAPH_ENTITY_DEBUG   (*this) << "This is a message of level MSG_TYPE_DEBUG\n";
+ DYNAMIC_GRAPH_ENTITY_INFO    (*this) << "This is a message of level MSG_TYPE_INFO\n";
+ DYNAMIC_GRAPH_ENTITY_WARNING (*this) << "This is a message of level MSG_TYPE_WARNING\n";
+ DYNAMIC_GRAPH_ENTITY_ERROR   (*this) << "This is a message of level MSG_TYPE_ERROR\n";
+ DYNAMIC_GRAPH_ENTITY_DEBUG_STREAM   (*this) << "This is a message of level MSG_TYPE_DEBUG_STREAM\n";
+ DYNAMIC_GRAPH_ENTITY_INFO_STREAM    (*this) << "This is a message of level MSG_TYPE_INFO_STREAM\n";
+ DYNAMIC_GRAPH_ENTITY_WARNING_STREAM (*this) << "This is a message of level MSG_TYPE_WARNING_STREAM\n";
+ DYNAMIC_GRAPH_ENTITY_ERROR_STREAM   (*this) << "This is a message of level MSG_TYPE_ERROR_STREAM\n";
+ \endcode
+ 
+
+   \note Thread safety. This class expects to have:
+   - only one reader: the one who take the log entries and write them somewhere.
+   - one writer at a time. Writing to the logs is **never** a blocking
+     operation. If the resource is busy, the log entry is discarded.
+*/