Adds 8 compass directions for the tile-build axis. Camera position,
corridor rotation, and refetch math all read from window.__flightDir.
Test URLs:
#flight=N north (default, +Z, current behaviour)
#flight=E east (+X)
#flight=S south (-Z)
#flight=W west (-X)
#flight=NE northeast (diagonal)
#flight=SE southeast
#flight=SW southwest
#flight=NW northwest
Renders with no hash unchanged. Each direction rotates the
corridor so its long axis follows the chosen compass bearing, and
the camera drifts along that bearing.
Richard Zink
9027099d89