signature_scheme lives in Session

not ConnectionFileMixin
mention metadata / display_data similarity in pyout spec
remove pylab from notebook doc
update nbconvert doc

update to new CLI

remove documentation of ill-advised `--script` option.
rename nbconvert doc to nbconvert.rst
add some detail in rst and markdown output
add pandoc note
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.
test KernelManager.get_connection_info
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
Merge pull request #3831 from minrk/nbdoc

update nbconvert doc with new CLI
Merge pull request #3828 from minrk/signature_scheme

signature_scheme lives in Session

not ConnectionFileMixin

prevents empty signature_scheme in connection files
warn on glob with no matches