Fix for #3719

%-d is not a valid strftime format on windows.
add delay to autosave in beforeunload

allows forceful 'discard changes' by reloading the page and dismissing the warning,
which @fperez really wanted today.
Nicer message when pandoc is missing, closes #3730
Merge pull request #3733 from ivanov/pandoc-missing

Nicer message when pandoc is missing, closes #3730
Change default build directory
Make sure the path exists that the figures are to be written to.
Don't move the file if it doesn't need to be moved.
Move extracted files into their own subdir
Added a space between pound and comments (@minrk request)
s/extractfigure.py/extractoutput.py
Rename ExtractFigureTransformer to ExtractOutputTransformer
FilesWriter now reads  key instead of
DebugWriter now reads  key instead of
Removed bad comment
Renamed remaining `figures` strings
Updated app tests
To look for output in local dir.
Added space between pund and comment
my attempt to fix #3735

an alternative to this would be to do something like
`\DeclareGraphicsExtensions{.pdf}` in the preamble
Merge pull request #3734 from jdfreder/file_subdir

Nbconvert: Export extracted files into `nbname_files` subdirectory

Default build directory changed to .
Files extracted from notebook now are placed into a ./notebook_files/ directory by default
Spaces added between # symbols and comments
It may be best to look at the diffs of the individual commits... The addition of spaces in the comments makes the overall diff hard to read.
better message when notebook format is not supported

Different messages for bad version and bad JSON.

closes #1592