Main

- Support for loadable Shadow Masks as proposed by Martin Donlon.

  you must download masks from https://github.com/MiSTer-devel/ShadowMasks_MiSTer and place to Shadow_Masks folder on SD card.

- input: fix keyboard to joystick mapping.

- user_io: fixes and tweaks in image I/O, support 2352 byte/sector for PSX core.

- improved screenshots (alanswx)