Moves some indexing-specific exceptions to zarr.errors, and ensures that all Zarr-specific
exception classes accept a pre-formatted string as a single argument. This is a breaking change to
the following exceptions classes: :class:`zarr.errors.BoundsCheckError`, :class:`zarr.errors.NegativeStepError`
:class:`zarr.errors.VindexInvalidSelectionError`. These classes previously generated internally
formatted error messages when given a single argument. After this change, formatting of the error
message is up to the routine invoking the error.