Directional bias

[mjrlowe]

Some algorithms could have functions that pick neighbor cells to connect to that aren't completely random. Some examples:

• Horizontal and vertical bias (e.g. picking a vertical neighbor is twice as likely as picking a horizontal neighbor)
• Pick neighbors according to a perlin/open-simplex noise function (creates blobby patterns)
• Other functions (see this p5.js sketch I made a while ago: change "select neighbor mode")
• Custom functions? It wood be cool if the user was able to give the algorithm a custom function to pick the neighbors with. (Maybe it takes in the cell's x and y position and it's possible neighbors and it outputs which neighbor/direction to chose?)

This will work best for algorithms like the recursive backtracker, where almost every step we have to make a decision about which neighbor we should connect to.

[mjrlowe]

Added this in version 0.4.0, using custom functions, but currently it is only compatible with some of the algorithms due to the way it is implemented.