short description: navigation enhancements: better error handling and fallback - you should never get a google error again, even if you run out of requests for the day. blacklist for failing navigation strategies - it now has a priority queue that it goes through to find the next best strategy. if a strategy fails, it will be blacklisted for the next hour. this is a performance fix also since previously it would keep hitting the failed service over and over, slowing down the bot. google -> mapzen -> yours -> default walking added mapzen navigation strategy. this is probably the best strategy since it has no daily limits once you have obtained a key, it looks pretty human, and it is fast and stable. the human navigation strategies we support now are: google (requires a key) ma