Zappend

Fixes

* Global metadata attributes of target dataset is no longer empty. (56)

* If the target _parent_ directory did not exist, an exception was raised
reporting that the lock file to be written does not exist. Changed this to
report that the target parent directory does not exist. (55)

Enhancements

* Added missing documentation of the `append_step` setting in the
[configuration reference](https://bcdev.github.io/zappend/config/).

Enhancements

* A new configuration setting `append_step` can be used to validate
the step sizes between the labels of a coordinate variable associated with
the append dimension. Its value can be a number for numerical labels
or a time delta value of the form `8h` (8 hours) or `2D` (two days) for
date/time labels. The value can also be negative. (21)

* The configuration setting `append_step` can take the special values
`"+"` and `"-"` which are used to verify that the labels are monotonically
increasing and decreasing, respectively. (20)

* It is now possible to reference environment variables
in configuration files using the syntax `${ENV_VAR}`. (36)

* Added a demo Notebook `examples/zappend-demo.ipynb` and linked
it by a binder badge in README.md. (47)

Fixes

* When `slice_source` was given as class or function and passed
to the `zappend()` function either as configuration entry or as keyword
argument, a `ValidationError` was accidentally raised. (49)

* Fixed an issue where an absolute lock file path was computed if the target
Zarr path was relative in the local filesystem, and had no parent directory.
(45)

Enhancements

* Allow for passing custom slice sources via the configuration.
The new configuration setting `slice_source` is the name of a class
derived from `zappend.api.SliceSource` or a function that creates an instance
of `zappend.api.SliceSource`. If `slice_source` is given, slices passed to
the zappend function or CLI command will be interpreted as parameter(s)
passed to the constructor of the specified class or the factory function.
(27)

* It is now possible to configure runtime profiling of the `zappend`
processing using the new configuration setting `profiling`. (39)

* Added `--version` option to CLI. (42)

* Using `sizes` instead of `dims` attribute of `xarray.Dataset` in
implementation code. (25)

* Enhanced documentation including docstrings of several Python API objects.

Fixes

* Fixed a problem where the underlying i/o stream of a persistent slice dataset
was closed immediately after opening the dataset. (31)

* Now logging ignored encodings on level DEBUG instead of WARNING because they
occur very likely when processing NetCDF files.

Enhancements

* Introduced _slice factories_
- Allow passing slice object factories to the `zappend()` function.
Main use case is to return instances of a custom `zappend.api.SliceSource`
implemented by users. (13)

- The utility functions `to_slice_factories` and `to_slice_factory`
exported by `zappend.api` ease passing inputs specific for a custom
`SliceSource` or other callables that can produce a slice object. (22)

* Introduced new configuration flag `persist_mem_slices`.
If set, in-memory `xr.Dataset` instances will be first persisted to a
temporary Zarr, then reopened, and then appended to the target dataset. (11)

* Added initial documentation. (17)

* Improved readability of generated configuration documentation.

* Using `requirements-dev.txt` for development package dependencies.

Fixes

* Fixed problem when passing slices opened from NetCDF files. The error was
`TypeError: VariableEncoding.__init__() got an unexpected keyword argument 'chunksizes'`.
(14)

* Fixed problem where info about closing slice was logged twice. (9)

Metadata fixes in `setup.cfg`. No actual code changes.

*The initial release.*