Write notebook server info file in security directory
Test for writing and removing server info files
Fix writing server info files on Python 2
Manually document py3compat module.

Automatic documentation doesn't work well with things that have
alternative definitions inside conditional blocks.
Fix "Source" text for the "Other Syntax" section of the notebook

Before it was shown as the "Display" one because of a missing end of
line.
warn when notebook is started in pylab mode

because it is always a bad idea
Added a math jinja macro containing the scripts to load mathjax.
Added missing braces.
check return types of formatters

and show error messages when formatters fail
validate that text display data is text

at DisplayObject construction time
Changed name of file from math to mathjax.
protect javascript from invalid mime-type data

everything is a string, if anything else is sent,
drop it so it doesn't show up in the notebook document.
handle (data, metadata) in @check_return
revert output area changes
validate output types in append_output

validates from files, as well as from kernels
xpects typo
test append_output with invalid data
Change location of mathjax macro.
image formatters allow both bytes and unicode (b64-encoded)
b64 unicode literals for images