Snapshots and tests

To see a layout at every screen size without resizing windows, render it headlessly into PNGs (phone, tablet, desktop):

odin run example -collection:lib=. -define:KILN_SNAPSHOT=true -define:START_PAGE=2

The files land in snapshots/. No window opens.

define	what
`KILN_SNAPSHOT=true`	snapshot build instead of a window
`KILN_SNAPSHOT_DIR=...`	where the PNGs go (default `snapshots`)
`KILN_SNAPSHOT_SIZES=phone,desktop`	which sizes to render (default `phone,tablet,desktop`)

Hooks

Config has snapshot hooks:

field	what
`snapshot_setup`	loads test data after `init` (gets the model as `rawptr`)
`snapshot_open`	renders an extra image per dialog / drawer
`snapshot_pointer`	hovers a point (tooltips)
`snapshot_clicks`	clicks before rendering (open popups)

Tasks run synchronously in snapshots, so the images are the same every time.

The demo exposes two of them:

odin run example -collection:lib=. -define:KILN_SNAPSHOT=true -define:START_PAGE=4 -define:SNAPSHOT_OPEN=reset

Tests run headlessly too:

odin test kiln -define:KILN_SNAPSHOT=true