Jupytext

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**Fixed**

- Sphinx format tested on `World population` notebook ([97](https://github.com/mwouts/jupytext/issues/97))
- Mirror test made stronger on this occasion!
- Markdown representation recognize Julia, Scheme and C++ code cells as such
- Light representation of Scheme and C++ notebooks fixed ([61](https://github.com/mwouts/jupytext/issues/61))

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**Added**

- All `jupytext` related metadata goes to a `jupytext` section ([91](https://github.com/mwouts/jupytext/issues/91)). Please make sure your collaborators use the same version of Jupytext, as the new version can read previous metadata, but not the opposite.
- Notebooks extensions can be prefixed with any prefix of at most three chars ([87](https://github.com/mwouts/jupytext/issues/87)).
- Export of the same notebook to multiple formats is now supported. To export to all python formats, plus `.ipynb` and `.md`, use `"jupytext": {"formats": "ipynb,pct.py:percent,lgt.py:light,spx.py:sphinx,md"},`.
- README includes a short section on how to extend `light` and `percent` formats to more languages ([61](https://github.com/mwouts/jupytext/issues/61)).
- Jupytext's contents manager accepts the `auto` extension in `default_jupytext_formats` ([93](https://github.com/mwouts/jupytext/issues/93)).
- All Jupyter magics are escaped in `light` scripts and R markdown documents. Escape magics in other formats with a `comment_magics` metadata (true or false), or with the contents manager `comment_magics` global flag ([94](https://github.com/mwouts/jupytext/issues/94)).

**Fixed**

- Trusting notebooks made functional again.
- Command line `jupytext` returns a meaningful error when no argument is given.
- Fixed global pairing configuration ([95](https://github.com/mwouts/jupytext/issues/95)).

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**Added**

- `light` and `percent` formats made available for scheme and cpp notebooks. Adding more formats is straightforward - just add a new entry to _SCRIPT_EXTENSIONS in languages.py, a sample notebook and a mirror test ([61](https://github.com/mwouts/jupytext/issues/61))
- Format name is automatically appended to extension in `jupytext_formats` when notebook is loaded/saved.

**Fixed**

- Notebooks extensions can only be prefixed with `.nb` ([87](https://github.com/mwouts/jupytext/issues/87))

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**Fixed**

- Markdown cells header in sphinx gallery format may have a space between first and following.

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**Added**

- Header for cells in `percent` format is more robust: use `[markdown]` and `[raw]` to identify cell types. Cell type comes after the cell title. ([59](https://github.com/mwouts/jupytext/issues/59))
- Jupytext can read and write notebooks as Hydrogen/VScode/Spyder/PyCharm compatible scripts (cells starting with ` %%`) ([59](https://github.com/mwouts/jupytext/issues/59))
- Jupytext can read and write notebooks as Sphinx-gallery compatible scripts ([80](https://github.com/mwouts/jupytext/issues/80))
- Metadata are supported for all cell types in light python and percent formats ([66](https://github.com/mwouts/jupytext/issues/66)). Due to this, light python format version is now 1.3. Light python notebooks in versions 1.1 and 1.2 are still readable.
- Command line `jupytext` has a `from` argument, and now accepts notebook from the standard input.

**Fixed**

- Fix merging of input and output notebooks ([83](https://github.com/mwouts/jupytext/issues/83))
- Removed extra new line on stdout in command line `jupytext` ([84](https://github.com/mwouts/jupytext/issues/84))

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**Added**

- Code lines that start with a quotation mark in Jupyter are commented in the corresponding Python and Julia scripts ([73](https://github.com/mwouts/jupytext/issues/73))
- Update pypy, add flake8 tests on Travis CI ([74](https://github.com/mwouts/jupytext/issues/74))

**Fixed**

- Import notebook.transutils before notebook.services.contents.filemanager ([75](https://github.com/mwouts/jupytext/issues/75))