tagged for the 2021 gdc demos (jam13, ku). includes backports for both builds, but excludes ku-specific changes (cursor disable, deprecated by 1c6970a, and trs from extras/staging).
as it is the first v2 release, this also contains the new extras headers (sprite, block, profiler), the alg v2 rewrite #22, the api rewrite #21, benchmark + perf improvements #23, new demos, and a number of fixes.