Preparing for 5.1-dev (#3550)

Adjusting raylib.h to reflect post-5.0 changes now.

src/raylib.h

@@ -1,6 +1,6 @@
 /**********************************************************************************************
 *
-*   raylib v5.0 - A simple and easy-to-use library to enjoy videogames programming (www.raylib.com)
+*   raylib v5.1-dev - A simple and easy-to-use library to enjoy videogames programming (www.raylib.com)
 *
 *   FEATURES:
 *       - NO external dependencies, all required libraries included with raylib
@@ -82,9 +82,9 @@
 #include <stdarg.h>     // Required for: va_list - Only used by TraceLogCallback
 
 #define RAYLIB_VERSION_MAJOR 5
-#define RAYLIB_VERSION_MINOR 0
+#define RAYLIB_VERSION_MINOR 1
 #define RAYLIB_VERSION_PATCH 0
-#define RAYLIB_VERSION  "5.0"
+#define RAYLIB_VERSION  "5.1-dev"
 
 // Function specifiers in case library is build/used as a shared library (Windows)
 // NOTE: Microsoft specifiers to tell compiler that symbols are imported/exported from a .dll