Ricecooker

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* Add ``ricecooker.utils.youtube``, containing utilities for handling and caching YouTube videos and playlists.
* Improve validation of ``m`` and ``n`` mastery model values in ``ExerciseNode``.

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* Remove SushiBar remote monitoring and remote command functionality

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* Documentation overhaul and refresh, see `ricecooker.readthedocs.io <https://ricecooker.readthedocs.io/>`__
* Add support for specifying a Channel tagline
* Ensure we send ``extra_fields`` data for all node types
* Make ``--reset`` behavior the default
* Remove legacy code around ``compatibiliry_mode`` and BaseChef class
* Improved caching logic (no caching for thumbnails and local paths, always cache youtube downloads)
* Ensure chefs clean up after run (automatic temp files removal)
* Added ``save_channel_tree_as_json`` full channel metadata as part of every run.
* Added support for web content archiving
* Further improvements to logging
* Bugfix: deep deterministic cache keys for nested dicts values in ``ffmpeg_settings``

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* Added ``--sample N`` command line option. Run script with ``--sample 10`` to
produce a test version of the channel with 10 randomly selected nodes from
the full channel. Use this to check transformations are working as expected.
* Added ``dryrun`` command. Use the command ``./sushichef.py dryrun`` to run the
chef as normal but skip the step where the files get uploaded to Studio.
* Added HTTP proxy functionality for YouTubeVideoFile and YouTubeSubtitleFile
Set the ``PROXY_LIST`` env variable to a ``;``-separated list of ``{ip}:{port}``.
Ricecooker will detect the presence of the ``PROXY_LIST`` and use it when
accessing resources via YoutubeDL. Alternatively, set ``USEPROXY`` env var
to use a list of free proxy servers, which are very slow and not reliable.
* Improved colored logging functionality and customizability of logging output.

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* Changed default behaviour to upload the staging tree instead of the main tree
* Added ``--deploy`` flag to reproduce old bahavior (upload to main tree)
* Added thumbnail generating methods for audio, HTML5, PDF, and ePub nodes.
Set the ``derive_thumbnail=True`` when creating the Node instance, or pass the
command line argument ``--thumbnails`` to generate thumbnails for all nodes.
Note: automatic thumbnail generation will only work if ``thumbnail`` is None.

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* Added support the ``h5p`` content kind and ``h5p`` file type
* Removed monkey-patching of ``localStorage`` and ``document.cookie``
in the helper method ``download_static_assets``
* Added validation logic for tags
* Improved error reporting