tests - support new pillow version with qoi writing

might as well as add rrect/rrectfill for 0.2.7 already

added another readme link in the webapp

fixed abs constfold (oops)

minor: handle unicode in cmdline consts; clarify const doc.; deprecat…

…e custom preprocessor

updated version 42

avoid bxBX after 0 when renaming (fixes #5)

minor readme updates

support local builtins (but add arg to disable them, like pico8 has),…

… minor-ish readme changes

also rename labels during minify (+ lint unused/dup labels)