Add optional server for sync render calls + fixes

Tag just for provoking tests, will be non-rc

Improve single-image write speed

Update README and CHANGELOG for v1 release (#344)

* update README for v1 release

* update changelog

* bump plotly min version in dev extra

Sanizite non alphanum characters from filenames

Pass `plotlyjs` arg from Kaleido to PageGenerator

Pass mathjax option to default plotly.js template

Add arg `kopts` to wrappers, to pass to Kaleido()

Fix various errors, see CHANGELOG.txt

Allow figure-like dict and fix bugs