[Ohrrpgce] wip r13876: Press T in the sprite editor to toggle onionskin overlay

[cron at rpg.hamsterrepublic.com]

https://github.com/ohrrpgce/ohrrpgce/commit/d1e089bb1ea56060ec8c499fd6607a186f55c463
Author: james <james at 7d344553-34f0-0310-a9b1-970ce8f1c3a2>
Date:   Sun Apr 6 23:59:35 2025 +0000

    Press T in the sprite editor to toggle onionskin overlay
    

 custom_udts.bi            |  2 ++
 drawing.bas               | 40 +++++++++++++++++++++++++++++++++++++++-
 ohrhelp/sprite_editor.txt |  3 +++
 whatsnew.txt              |  4 +++-
 4 files changed, 47 insertions(+), 2 deletions(-)