Dantro

- !83 Takes care of a deprecation warning regarding imports from the `collections` module.

- Infrastructure and Documentation
- 43 Add a Sphinx-based documentation, currently containing only the API reference
- 44 makes the dantro version number single-sourced in `dantro/__init__.py`

- Many new `PlotManager` and `PlotCreator` features:
- With 40 and !41, the `PlotManager` can auto-detect which plot creator is to be used; this allows to leave out the `creator` key in the plot configuration and thus simplifies the configuration of a plot.
- 63 greatly extends the configuration capabilities of the `PlotManager`: There now is a so-called "base" configuration, which plot configurations can use to base their parameters on; this is done via the `based_on` key.
- 69 Allows `based_on` to be a sequence of base configuration names that are accumulated and then used as basis for the new plot.

- A new `PlotHelper` framework for the `ExternalPlotCreator`:
- 46 allows the `ExternalPlotCreator` to enter a matplotlib RC parameter context in which a certain style is set.
- 45 implements the `PlotHelper`, which provides a configuration-accessible interface for matplotlib functions invoked via `ExternalPlotCreator`.
- 62 implements `PlotHelper` functions to set title, labels, limits, scale, legend, horizontal and vertical lines.
- 64 adds the possibility to conveniently create animations when using the `ExternalPlotCreator` in combination with the `PlotHelper`
- 68 makes the `PlotHelper` work axis-specific and thus allow defining helpers for different axes of a figure with subplots.
- !72 extends `PlotHelper` capabilities and improves error messages

- New data container and proxy features:
- 47 adds the `XrDataContainer`, which stores data as an [`xarray.DataArray`](http://xarray.pydata.org/en/stable/data-structures.html#dataarray) and associated dimension labels and coordinates by looking at the container attributes
- 66 implements proxy support for `XrDataContainer`
- 71 enables to reinstate a previously resolved proxy, thereby releasing the existing data, allowing it to go out of memory

- Miscellaneous improvements and tweaks
- !39 makes minor improvements to info strings
- 51 adds a `tree` property to `BaseDataGroup`, which returns the tree representation string of that group.
- 54 lets HDF5 loader automatically convert encoded strings into python strings
- 60 removes unnecessary log messages upon entering/exiting a data container's or group's `__init__` method.
- 61, !53 makes `BaseDataContainer.__init__` non-abstract, which is not only more convenient but also more consistent (`BaseDataGroup` is not abstract either.) This also improves modularization of the `mixins` module.

- !44 Fixes a bug where the association of parameter dimensions in `UniversePlotCreator` was wrong and could lead to failing plots.

- 36 and !36 make the `out_dir` of `DataManager` more configurable and adds some other minor tweaks.
It renames the format string segment `date` to `timestamp` (to be more general) and adds the `cfg_exists_action` argument to `PlotManager`, which allows to control the behaviour upon.
Furthermore, the `read_yml` and `write_yml` functions now allow selecting a file mode.
- !37 adds the ability to specify a default type for the `new_container`
function of `BaseDataGroup`. This choice is also respected by the HDF5
loader, thus allowing a parent group to specify its childrens' type and not
requiring them to use the mapping feature to be loaded as a custom type.
- !38 removes the edge and node attribute related features from `NetworkGroup`,
because they do not work in a general enough manner.

- 35 makes changes to `NetworkGroup` to concur to the NetworkX interface and adds some tweaks to the `set_node_attributes` function.
- !35 allows matplotlib versions larger than the (python2 backwards compatible) version 2.2.3, which is important to keep up with new matplotlib features.

- !33 allows using transposed edge specifications in `NetworkGroup` for creation of an `nx.Graph`