Async breadth first search for node

Usage

var bfs = require(bfs);
bfs(starts, movefn, goalfn, callback);

where

• start - array of possible start positions
• movefn - function(depth, node, callback) - a function called to retreive nodes connected to the specified node
  • callback should be called with the new nodes callback(err, newNodes)
• goalfn - function(node, callback) - a function called to check if the node is a valid goal.
  • callback should be called with true or false callback(err, true|false)
• callback - function(err, path)
  • path - the shortest path found.