Allow creation of islands at specific distances from home

* Better distribution of islands, too.
Bigger islands
Fix bug where island seed doesn't have landMass attr
Add u.distance() fn for dist between two points
Spawn some people to rescue at incremental dists from mary
Rename genLastPersonCenter() to genLostPersonCenter()
Make block type arrays available before seeding
Fix code to make it actually spawn mary in clear area
Gen random food-rich island closeish to mary start