Add docs for entities

sea_transport/entities/IEntity.h

@@ -4,10 +4,20 @@
 #include "ISerializable.h"
 
 
+//! Alias type for any entity ID
 typedef unsigned long long entity_id;
 
+/**
+ * @brief Base interface for all entities
+ * 
+ */
 class IEntity : public ISerializable {
 public:
+   /**
+    * @brief Getter function for entity identificator
+    * 
+    * @return entity_id entity identficator
+    */
    virtual entity_id id() const = 0;
 };