1.6.0

• Added new caching behavior that allows a cache to return a hit, while telling tilestrata it should regenerate a tile in the background for the next person. The use case: you have tile that's old enough it should be regenerated, but it's not old enough to warrant making the user wait for a new tile to be rendered. To accomplish this in a plugin, have get() return true as the fourth argument to the callback. Read more about it in the readme.