- `Pixel` now has a field `soiltype`

- read soil type information from tiff file

Rename this function to `showlandscape()`.

(Not yet tested.)

closes #85

Also updated CONTRIBUTORS.md, added a "none" option for
`core.logoutput`, and added type annotations to the Skylark struct

As well as the concomitant macros, and @killother

This used to be done by Agents.jl, is now done natively

I now use parametric methods to store initialised parameter structs,
rather than creating a special registry for these with a closure.

Still need to write tests to make sure it works properly, but at least
it runs without errors now and seems to do what it's supposed to.

Compile time still increased to 50s (from 15s), but at the moment I
can just about live with that.

This closes #24.

This is a major commit, probably rather too large, but anyway. There
are no tests yet, so no guarantee for correctness. But it's good
progress :-)

It is now contained within a single function that can be called at
need, rather than being calculated every day for every pixel.

Closes #52

This commit includes a `sed` pass over all files to change all
occurrences of the former spelling "Persephone" to "Persefone":
`sed -ie "s/Persephone/Persefone/" *`

This is a major change to the codebase. I'm not entirely convinced yet
that it actually makes sense, but overall I think the benefits
outweigh the problems. Closes issue #37.

Not yet functional - the necessary functions still need to be implemented.

Translated the Wolpertinger to the new syntax, Wyvern to follow later.

Not yet functional!