added `{ preserveDrawingBuffer: true }` to the webgl2 context creation, now Firefox right click Save Image works properly (previously it saved a 100% transparent image).

apparently this can cause performance issues especially on mobile, so I will see about adding a different way to save later.

also made it update the URL hash automatically when adding inflection points (previously only on manual button click). this avoids losing work when accidentally refreshing the page etc. can't make it update on every action (zoom, pan, colours, ...) otherwise browser complains about too much history spam.

here are five things in a 2/5 Julia set: disk, line, three tree variants (distinguished by how they attach to the whole). not very refined (only 3 steps of each, 16 inflection points total including the initial Julia set location).