Version 0.2.3

Fixed rmarkdown converter for nbconvert, and tests, on older platforms

Version 0.2.2

• RMarkdown exporter for nbconvert (use it with: jupyter nbconvert --to rmarkdown notebook.ipynb)
• Parsing of R options now robust to parenthesis
• Jupyter cell tags are preserved in conversions
• requirements.txt now included in pypi package

Version 0.2.1

• Allows edition R markdown and markdown files in Jupyter
• Rmd cell options directly mapped to cell metadata
• New (default) pre-save hook update_selected_formats that saves to formats in metadata 'nbrmd_formats'
• Coverage increased