This was just supposed to be a new feature for the generic image tool (dithering support), but while working on that things kind of snowballed 😅
* Added dithering support to the generic image tool and the boot logo changer, when converting images to RGB565 format. This uses a Bayer 8x8 matrix, and the overall "strength" of the dither can be controlled - it defaults to what I feel is a sane value. Dithering can help reduce banding effects due to the low colour depth in RGB565.
* Made "fix" scaling mode more flexible in the generic image tool - now there's checkboxes beside the width and height dimensions - if you un-check one, the other dimension will be calculated automatically to keep the input's aspect ratio intact
* Improved downscaling quality in the generic image tool. While working on the dithering feature, I discovered the previous "gaussian resampling" downscaling method I was using introduced distortion in certain situations. I had a lot of fun playing around with possible replacements (I tried 10 new downscaling functions!), and finally settled on a hybrid function that mixes powers-of-two downscaling (with some custom mipmap style cross-blending) with Hermite interpolation. This new method is reasonably quick, gives clean results with no great distortion, and works well with alpha channels (doesn't introduce any dark fringing)
* Generic image tool now shows the dimensions of the output image
* Added a max width on the main tool page bodies, so that they don't get so wide on full-screen desktop browsers
* Fixed a few edge-case logic bugs here and there (e.g., when upscaling only a single dimensions with the generic image tool, or places where I thought I was copying objects, but was only creating references to them, etc.)
* Switched from using "var" declarations across all tool codebases to "let" or "const" instead
* Switched out the SVG alert icons to just use emoji instead
* Various other nips and tucks (fixed up my arbitrary 80-column comment wrapping on the tools that had previously just been eye-balled, fixed a few comment typos, etc.)
There was a lot of repeated JS across all my tools (e.g., image conversion, BIOS hash checking, etc.), and so I decided to move all shared code out to its own separate library. This will improve scalability and maintainability at the cost of portability - a fair trade in my opinion.
This work also involved large-scale refactoring of all of the tools. There's no actual functional difference (all the tools should behave exactly the same), bar some UI improvements for the oldest tools as a result of moving to the same codebase used by the more recent tools.
