stop wasting bytes decoding PLTE, support indexed transparency

(cherry picked from commit a38fca5)

version locking makes sense sometimes

port latest changes to deno

port latest changes to deno

readme test: fix decoding file on deno

roundCorners

(cherry picked from commit 9d85c16)

multi-point gradients

(cherry picked from commit 0b07810)

png: IDX support

(cherry picked from commit 9a9a8e7)

fix automatic conversion (532f9e6)

port jpeg decoding test to deno