Initial bias alteration

Adding bias to A-star so it favours longer already-discovered paths, and
debugging code to print the efficiency.
Bias fine-tuning

Varying the bias to find a better value that still finds the best paths
on the initial station.
Wholesale A-star replacement

An, on average, 50% reduction in evaluated turfs!

A lot of the file is still inefficient compared to the existing one.
A-star cleanup

A massive improvement to my version that includes design patterns from
the previous version, but that doesn't alter the produced paths or time
taken/turfs checked to find them (which are still better than the
original A-star, mind you)
Bias fine-tuning

Surprisingly, the default mulebot paths still work exactly the same,
except taking (on average) 35% of the 'time' of the original A-star
function. Wow!

This isn't necessarily the best value but I'll commit this for now.
File tidying

Commenting or deleting debugging code, updating indents/etc to conform
with code standards, improving comments.
Cleaning up A-star

Removing some commented-out code that needs further work, and adding a
few sanity checks to avoid runtime errors and worst-case scenarios.