Use separate sub-seeds for maze and food generation

[Debilski]

I think we should be able to specify a different food seed on the command line, especially when testing. Sometimes I just want to check if there is an anomaly in the food-creation algorithm but it is impossible to find out as any seed change also changes the layout.

Maybe --seed 13457898 will find a default food seed but using --seed 13457898:12345 we can manually add one.

[Debilski]

In addition to this: Perhaps we could instead of a seed, auto-generate a ‘layout generation string’ which encodes the seed for the layout creation as well as the size of the maze. This would allow us to simply share a layout with a string, without having to additionally specify the size of the layout.