added logging module and a sandbox project

include/matador/logger/log_level.hpp

@@ -0,0 +1,43 @@
+#ifndef MATADOR_LOG_LEVEL_HPP
+#define MATADOR_LOG_LEVEL_HPP
+
+#include <iosfwd>
+
+namespace matador::logger {
+
+/**
+ * Represents all available log levels
+ */
+enum class log_level
+{
+  LVL_FATAL,  /**< If a serious error occurred, use FATAL level */
+  LVL_ERROR,  /**< On error use ERROR level */
+  LVL_WARN,   /**< Warnings should use WARN level */
+  LVL_INFO,   /**< Information should go with INFO level */
+  LVL_DEBUG,  /**< Debug output should use DEBUG level */
+  LVL_TRACE,  /**< Trace information should use TRACE level */
+  LVL_ALL     /**< This level represents all log levels and should be used for logging */
+};
+
+/**
+ * Write log level in a human-readable string
+ * to a given std::ostream.
+ *
+ * @param os std::stream to write to
+ * @param lvl Log level to write
+ * @return The std::ostream
+ */
+std::ostream& operator<<(std::ostream &os, log_level lvl);
+
+/// @cond MATADOR_DEV
+
+struct log_level_range
+{
+  log_level min_level = log_level::LVL_INFO;
+  log_level max_level = log_level::LVL_FATAL;
+};
+
+/// @endcond
+
+}
+#endif //MATADOR_LOG_LEVEL_HPP