Qmflows

New
* Introduced a flag for keeping the Log files

Fix
* Improve CP2K error reporting (209)

New
* Added tests for generating the Sphinx documentation.

Changed
* Replaced ``requirements.txt`` with ``.readthedocs.yml``.
* Fixed the jupyter notebook in the documentation.

New
* Allow other cp2k executable: ``cp2k.sopt``, ``cp2k.psmp``, etc.

Changed
* Exposed ``InitRestart`` to the main QMFlows ``__init__.py`` file.
* Exchanged ``plams.init()`` / ``plams.finish()`` for ``qmflows.InitRestart`` in the ``qmflows.run()`` function.
* Store the ``cache.db`` file in the PLAMS working directory.

Added
* Introduced the ``CP2KMM`` class for classical forcefield calculations with CP2K: [qmflows/pull/150](https://github.com/SCM-NV/qmflows/pull/150).
* Introduced the ``PackageWrapper`` class: [qmflows/pull/149](https://github.com/SCM-NV/qmflows/pull/149).
* Introduced updates and code-style improvements to the ``Package`` and ``Result`` classes: [qmflows/pull/146](https://github.com/SCM-NV/qmflows/pull/146)
* Added workflow for [GitHub Actions](https://github.com/SCM-NV/qmflows/actions)

Removed
* [Removed references to Dirac](https://github.com/SCM-NV/qmflows/issues/152)
* [Removed Pymonad](https://github.com/SCM-NV/qmflows/issues/156)
* Remove support for [FDE](https://github.com/SCM-NV/qmflows/issues/171)

Changed
* Used [Path](https://github.com/SCM-NV/qmflows/issues/153) instead of ``str``.

Changed
* Use autopep to format the code

Removed
* Interface to HDF5
* Turbomol Parser
* graphviz dependency