update flow-syntax and supermd

- flow-syntax was updated primarily to fix a bug in superhtml and to
  get the latest version of ziggy.

- the supermd update fixes a crash when parsing "/" urls and introduces
  `$link.site()`, smd counterpart to superhtml's `$site.link()`

closes #179

update zine version

bump zine version

fix build asset install & upgrade to writergate

only took 6h45m to upgrade to writergate :^)

also build assets now install correctly

update zig-afl-kit

DateTime: add ability to add and subtract durations from a DateTime

Add `in` to DateTime for changing Time Zone

replace katex with temml in the sample website

do not append url_path_prefix when installing assets

increase 200x the image buffer size for wuffs

Previously Wuffs would fail to detect image size
when loading images becaeuse the buffer size provided
was too small.

This commit empirically solved all wuffs failures
on my personal webise, although we should find a
better way of deciding what's an appropriate size
for this buffer.