Rearranged htmlnotebook.txt
Added key distinction between Notebook app and notebook documents via capitalization. Added info on different cell types and sketch of plotting
Moved htmlnotebook.txt to htmlnotebook.rst to use GitHub rendering
Moved connecting to kernel section to how to's
Clarified that 'notebook' also refers to the state of the computation inside the Notebook, but that this is the same as the content of the .ipynb file
Added input cells and basic workflow sections
Types of input cell
Magic commands section
Plotting section
Interrupting and restarting added in basic workflow
Magics
Deleted section on printing, which is no longer valid. Renamed 'exporting' to 'saving' and moved to Basic workflow. Renamed 'basic concepts' to 'user interface'.
nbconvert
Finished first pass of refactoring
Editing of main features
Rewrote introduction. Introduced concept of *notebook space* and discussion of why the same word 'notebook' is used both for the notebook space and the corresponding notebook document
Features
add auth and paged request to gh_api
attempt to cache gh_api requests

with requests-cache
raise AttributeError on missing attribute in ShimModule

required for sphinx build to succeed