Actually only filter out PRODID key

It might happen that we filter out a SUMMARY line or similar which
coincidentally contains "PRODID"
Update ancient parts of the documentation

The ssl_verify param is a legacy from khal's wiki page.
Move class inspection code to utils
Change error formatting to not use **locals()
Add link to list of supported storages
Add width and height to image tags

Readthedocs' theme is trying so hard to be completely responsive, it
scales these badges up to 100% of the viewport width
Copy content of readme to docs

Because their content is going to diverge anyway
Fix formatting issues
Shorten doc text
Directory checking for singlefilestorage
remove uninteresting stuff from conf.py
Style fixes
Fix formatting
Title case for everything
Add tutorial
This is already in the README
Formatting fix
Rename storages to api.rst
Fix headline level
More doc updates