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)

Full Changelog: v0.5.1...v0.6.0