add unformal Name for 1.0
unformal name -> codename
mention metadata / display_data similarity in pyout spec
new util that also passes back the returncode
test for get_output_error_code
updated tests to use get_output_error_code
allow for List traitlets to come from command line
all nbconvert tests pass with pandoc
the last set of pandoc-dependent test
move ipython command line logic to one place

it keeps getting repeated, more elegant to move it out into the call
prevent profile_dir from being undefined

can happen when other traits are configured that depend on profile_dir,
e.g. `NotebookApp.extra_static_paths`.

This ensures that `init_profile_dir` fires prior to any reference
to the profile directory.
update payload source

should be simple key, not Python (or worse, IPython) specific long key.

I could have sworn I did this long ago,
but apparently the source key was only updated in display_data,
not execute_reply.
maintain instances of exporters for use in export_by_name

avoids recreating new Exporters every time
add basic logging to NbConvert stages
Parse markdown correctly when mathjax is disabled
don't reload template on every export

only load template if self.template doesn't exist
more default_config into Exporter._config_changed
propagate new values to singletons in export_by_name
tweak support-file output

move individual file output to debug level
add bytes-written
docstrings