Wholesale A-star replacement

I wish I'd just been able to update the original version, but something
kept going wrong.

This version creates paths of identical lengths (not necessarily the
same paths!) while evaluating, on average, only 35% of the tiles that
the original algorithm would. Seems like a decent improvement.

Also fixes some grammar in the mulebot file.
A-star fixes

Will obey the maxnodes parameter if it's provided (although perhaps not
in the way that it was originally meant?) The only one that uses it is
disease, and it wasn't an issue there, but at least in future it won't
be a problem.

Also slightly increased the maximum loop count from 1500 to 1800, on the
off-chance that the previous value was pessimistically low. In the
initial station this doesn't go past 1000, but if bots understand doors
their paths might get squiggly.
Minor modifications to Yvar's A* fixes:
-Removed the priorityqueue datum. It is now a list()
-priorityqueue/proc/insert is now a helper /proc/sorted_insert() as it may be helpful in maintaining pre-sorted lists or insertion sorts.
-Replaced priorityqueue/proc/extract_last() calls with calls to pop(), which already existed.
-Removed last few references to "bestF" (from old awful A) in lighting and MC
-Replaced a section were it'd append to the end of the returned path list and then reverse the list. Now it inserts at the start of the list.
Merge pull request #1 from Carn/AstarReview

Minor modifications to Yvar's A* fixes
Merge pull request #592 from Yvar/Astarfix

A-star replacement