v1.6.0

Added

• Every level's board without its answer: @johnmorrisdotca/tsunagi/layouts, TSUNAGI_LAYOUTS (by size, in level
  order) and TSUNAGI_PORTAL_LAYOUTS. A server that checks a solve, or lists who solved which level, knows a level by its
  board and never needs its answer, and the answers are over half of every size's file; the layouts of all 2,624 levels
  are about a third of the bytes of the levels. Made by node scripts/tsunagi-layouts.ts, held to the level files by
  layouts.test.ts. Nothing that was exported has changed.