Use 1-D Vec to be faster

1D vectors are faster and use less memory compared to 2D vectors

https://stackoverflow.com/questions/17259877/1d-or-2d-array-whats-faster

Would you be open to a PR that rewrites the library to use 1D vectors instead? This would obviously be a breaking change.

If so, do you think it's a better idea to use an existing crate like https://docs.rs/array2d/latest/array2d/index.html or just implement the basic logic needed by hand?