Better HUD adjusting option

[NVT_06]

The game features, at the moment, a Center HUD option for moving all the HUD to the center of the screen horizontally; this can be useful for those screens that for some reason crop the displayed image on the sides. However, in some cases, the image gets cropped on the upper al lower sides of a screen too, and there's no option to center the HUD vertically.

It would be nice to improve this option, for example by replacing Center HUD with two options like Adjust HUD X-axis and Adjust HUD Y-axis. In the rvgl.ini file, the CenterHud string could be replaced by something like HudPosX and HudPosY

Also, when switching to 4:3 ratio, the option is hidden automatically, but again, there are cases that require some tweaking on both X and Y axes, so I think it should be possible to change these two values at any resolution and aspect ratio.

This small improvement could be useful for those who, for example, want to run RVGL on older screens such as CRTs without compromises and without the need to manually fix the screen overscan, which sometimes isn't even possible (at least in a safe and easy way).

Thank you in advice!