Enhancements
* Added configuration setting `force_new`, which forces creation of a new
target dataset. An existing target dataset (and its lock) will be
permanently deleted before appending of slice datasets begins. (72)
* Chunk sizes can now be `null` for a given dimension. In this case the actual
chunk size used is the size of the array's shape in that dimension. (77)
API Changes
* Simplified writing of custom slice sources for users. The configuration setting
`slice_source` can now be a `SliceSource` class or any function that returns a
_slice item_: a local file path or URI, an `xarray.Dataset`,
a `SliceSource` object.
Dropped concept of _slice factories_ entirely, including functions
`to_slice_factory()` and `to_slice_factories()`. (78)
* Extracted `Config` class out of `Context` and made available via new
`Context.config: Config` property. The change concerns any usages of the
`ctx: Context` argument passed to user slice factories. (74)