See the doc comments in `common/src/vol.rs` for more information on
the API itself.
The changes include:
* Consistent `Err`/`Error` naming.
* Types are named `...Error`.
* `enum` variants are named `...Err`.
* Rename `VolMap{2d, 3d}` -> `VolGrid{2d, 3d}`. This is in preparation
to an upcoming change where a “map” in the game related sense will
be added.
* Add volume iterators. There are two types of them:
* _Position_ iterators obtained from the trait `IntoPosIterator`
using the method
`fn pos_iter(self, lower_bound: Vec3<i32>, upper_bound: Vec3<i32>) -> ...`
which returns an iterator over `Vec3<i32>`.
* _Volume_ iterators obtained from the trait `IntoVolIterator`
using the method
`fn vol_iter(self, lower_bound: Vec3<i32>, upper_bound: Vec3<i32>) -> ...`
which returns an iterator over `(Vec3<i32>, &Self::Vox)`.
Those traits will usually be implemented by references to volume
types (i.e. `impl IntoVolIterator<'a> for &'a T` where `T` is some
type which usually implements several volume traits, such as `Chunk`).
* _Position_ iterators iterate over the positions valid for that
volume.
* _Volume_ iterators do the same but return not only the position
but also the voxel at that position, in each iteration.
* Introduce trait `RectSizedVol` for the use case which we have with
`Chonk`: A `Chonk` is sized only in x and y direction.
* Introduce traits `RasterableVol`, `RectRasterableVol`
* `RasterableVol` represents a volume that is compile-time sized and has
its lower bound at `(0, 0, 0)`. The name `RasterableVol` was chosen
because such a volume can be used with `VolGrid3d`.
* `RectRasterableVol` represents a volume that is compile-time sized at
least in x and y direction and has its lower bound at `(0, 0, z)`.
There's no requirement on he lower bound or size in z direction.
The name `RectRasterableVol` was chosen because such a volume can be
used with `VolGrid2d`.
