summary plugin migration

[mirekdlugosz]

Using instructions from drafted blog post, I managed to port summary plugin to namespaced structure. I keep results of my work on my Github account, in migration branch: https://github.com/mirekdlugosz/pelican-plugins-summary/tree/migrate

I have not yet run code styling tools on this repo. I used new version of plugin in my website and confirmed it does not result in regressions on my posts.

[astrojuanlu]

Also, this plugin has not yet been uploaded to PyPI, right?

[mirekdlugosz]

@astrojuanlu no, it has not. At least not by me. As part of plugin migration, after creating new repository in plugins org, Justin should add PyPI key, so autobot can create and upload package for us.