Do not wrap headers in markdown.tpl because inconsistency in the interpretation of multiline headers.
don't blacklist builtin names

it is wholly appropriate for a class to have a `format` trait, or similar, but Config prohibits it.

This just removes that prohibition.
Corrected a typo in the format string for strftime
Merge pull request #3577 from Carreau/simple-mode

Simplify codemirror ipython-mode

make it a subset of python mode, only with configuration
Merge pull request #3531 from minrk/headingmath

allow markdown in heading cells
Merge pull request #3565 from Carreau/style-min

style.min.css shoudl always exist... don't silently fail.
Merge pull request #3567 from Carreau/app-init-event

Trigger a single event on js app initilized.
Merge pull request #3569 from minrk/pythonstartup

add PYTHONSTARTUP to startup files
Merge pull request #3575 from minrk/run-d

tweak `run -d` message to 'continue execution'

clarify any ambiguity with 'start'.
Merge pull request #3576 from damianavila/header_markdown

Added support for markdown in heading cells when they are nbconverted.
Merge pull request #3581 from damianavila/custom_css

Added the possibility to read a custom.css file for tweaking the final html in full_html and reveal templates.
update config builtins test
remove max_msg_size altogether

It was a security feature without an application.
add nbconvert.utils.pandoc

single entry point for calling pandoc for transforms.
add markdown2html filter

uses pandoc instead of Python markdown for better consistency.

Also eliminates one dependency.
Add __init__.py for sphinxext
Merge pull request #3590 from ariddell/master

IPython.sphinxext needs an __init__.py
Refer to Setuptools instead of Distribute
Merge pull request #3591 from cgohlke/patch-1

Refer to Setuptools instead of Distribute

Distribute is no more.
Merge pull request #3560 from minrk/longcell

Remove max_msg_size

The max_msg_size safety limit is just removed.

closes #3124