Fix duplicate log messages

No more duplicate messages in the log file if your workflow instantiates multiple Workflow instances.

Add background tasks

New features 

• workflow.background module to simplify launching background tasks (daemons)

Add diacritic folding

New features 

• Workflow.filter() now folds diacritics in search keys if query contains only ASCII characters, so that boll will match Böll etc.

Changes 

• Workflow.filter() now defaults to MATCH_ALL ^ MATCH_ALLCHARS to provide more relevant results much more quickly.

Bugfixes 

• Fixed a few typos in the documentation.