SST Beta 0.18 (a.k.a. Shockingly Small Thing)

In perhaps our most avoidably delayed and most childishly named update
yet, we finally introduce all the major internal overhauls I did earlier
this year (and late last year...) to a public release, along with
exactly two new user-facing features: 4104 autojump, and a basic
replacement for speedrun_demorecord. The latter will be improved later,
and there's also a whole bunch of additional work not included, mostly
pertaining to HUD stuff. I'll need to do more on that, when I eventually
find the time.

Thanks, and have fun!  :^)