Got most of the terrain parameters close to good values.

-Peter Mawhorter
Work on a wrinkle in the noise system. It seems like interpolation of
the surflet values has a small edge in it which becomes visible at
continental scales.

-Peter Mawhorter
Managed to get a zoomed noise setup that shows some sharp lines that
shouldn't be there.

-Peter Mawhorter
Figured out what was almost certainly the cause of my problem: I was
adding a very large offset to a floating point number that was varying
over a very tiny range (due to the extremely low frequency of the
continents). Now all noise functions accept a "salt" parameter, so you
shouldn't have to add offsets in order to get variation in patterns.
Still need to rewrite all of the rest of the code to pass those
arguments though.

-Peter Mawhorter