raylib-d how to program a simple moving circle.

[Alain De Vos]

vscode no longer complains.

But "dub run" gives,

```

  dub run
     Starting Performing "debug" build using /usr/bin/dmd for 
x86_64.
   Up-to-date raylib-d 5.5.1: target for configuration [library] 
is up to date.
     Building myprogram ~master: building configuration 
[application]
      Linking myprogram
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /home/x/.dub/cache/myprogram/~master/build/application-debug-UNjmUV2QooI2uGdw4N2cYw/myprogram.o: in function `_Dmain':
/mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:16:(.text._Dmain[_Dmain]+0xe): undefined reference to `WindowShouldClose'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:22:(.text._Dmain[_Dmain]+0x1b): undefined reference to `BeginDrawing'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:23:(.text._Dmain[_Dmain]+0x34): undefined reference to `ClearBackground'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:26:(.text._Dmain[_Dmain]+0x5c): undefined reference to `DrawText'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:29:(.text._Dmain[_Dmain]+0x83): undefined reference to `DrawRectangle'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:32:(.text._Dmain[_Dmain]+0xad): undefined reference to `DrawCircle'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:38:(.text._Dmain[_Dmain]+0xb2): undefined reference to `EndDrawing'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /mnt/xxx_source/Languages_ok/dlangtut/dub/69_raylib_error/source/app.d:45:(.text._Dmain[_Dmain]+0xbc): undefined reference to `CloseWindow'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /home/x/.dub/cache/raylib-d/5.5.1/build/library-debug-VCS2IbF0QjMRz7j1LmY9HA/libraylib-d.a(binding_1_868.o): in function `_D6raylib7binding21validateRaylibBindingFNbNiZv':
/home/x/.dub/packages/raylib-d/5.5.1/raylib-d/source/raylib/binding.d:27:(.text._D6raylib7binding21validateRaylibBindingFNbNiZv[_D6raylib7binding21validateRaylibBindingFNbNiZv]+0x11): undefined reference to `raylib_version'
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /home/x/.dub/packages/raylib-d/5.5.1/raylib-d/source/raylib/binding.d:27:(.text._D6raylib7binding21validateRaylibBindingFNbNiZv[_D6raylib7binding21validateRaylibBindingFNbNiZv]+0x24): undefined reference to `raylib_version'
collect2: error: ld returned 1 exit status
Error: undefined reference to `WindowShouldClose`
        referenced from `_Dmain`
Error: undefined reference to `BeginDrawing`
        referenced from `_Dmain`
Error: undefined reference to `ClearBackground`
        referenced from `_Dmain`
Error: undefined reference to `DrawText`
        referenced from `_Dmain`
Error: undefined reference to `DrawRectangle`
        referenced from `_Dmain`
Error: undefined reference to `DrawCircle`
        referenced from `_Dmain`
Error: undefined reference to `EndDrawing`
        referenced from `_Dmain`
Error: undefined reference to `CloseWindow`
        referenced from `_Dmain`
Error: undefined reference to `raylib_version`
        referenced from `nothrow @nogc void 
raylib.binding.validateRaylibBinding()`
Error: undefined reference to `raylib_version`
        referenced from `nothrow @nogc void 
raylib.binding.validateRaylibBinding()`
        perhaps a library needs to be added with the `-L` flag or 
`pragma(lib, ...)`
Error: linker exited with status 1
        cc 
/home/x/.dub/cache/myprogram/~master/build/application-debug-UNjmUV2QooI2uGdw4N2cYw/myprogram.o -o /home/x/.dub/cache/myprogram/~master/build/application-debug-UNjmUV2QooI2uGdw4N2cYw/myprogram -g -m64 -Xlinker --no-as-needed -Xlinker --export-dynamic -Xlinker -rpath=/usr/lib/dmd/2.109/lib64 /home/x/.dub/cache/raylib-d/5.5.1/build/library-debug-VCS2IbF0QjMRz7j1LmY9HA/libraylib-d.a -L/usr/lib/dmd/2.109/lib64 -lphobos2 -lpthread -lm -lrt -ldl
Error /usr/bin/dmd failed with exit code 1.


```