Changelog entries for switchable crop models

CHANGELOG.md

@@ -23,12 +23,42 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.5.3] - unreleased
 
-*Plan: code restructuring to allow multiple crop models (#70)*
+**Switchable crop models (#70)**
 
 ### Added
 
+- Support for switchable crop models (#70), crop models can be set
+  with the `cropmodel` setting in the `[crop]` section of
+  `parameters.toml`.
+
+- New submodules `ALMaSS` for the ALMaSS crop model, and `SimpleCrop`
+  for testing switchable crop models.
+
 ### Changed
 
+- All functionality specific to the ALMaSS crop model has been moved
+  to the submodule `ALMaSS`.
+
+- Due to switchable crop models, some types are now parametric:
+  `AgricultureModel{Tcroptype,Tcropstate}` and `FarmPlot{Tcropstate}`.
+
+- `FarmPlot{Tcropstate}` now only stores basic information about which
+  pixels are part of the farm plot, all crop-specific information is
+  now stored in the field `cropstate`.  Many functions acting on a
+  `FarmPlot` now mostly forward to functions of the same name acting
+  on the `cropstate` field of a `FarmPlot`.
+
+- The type of `height` in `ALMaSS.CropState` and
+  `ALMaSS.CropCurveParams` is now a unitful number `::Length{Float64}`.
+
+- Both crop models `ALMaSS` and `SimpleCrop` now also support the
+  functions `cropcover` and `cropyield` in addition to `croptype`,
+  `cropname`, `cropheight`.
+
+- `cropheight` now returns a unitful number `::Length{Float64}`, and
+  returns height `0cm` if the landscape at that position is not a
+  `FarmPlot`.
+
 ### Deprecated
 
 ### Removed