Replace tags at config time instead of every write

This fixes:
    UnboundLocalError: local variable 'tags' referenced before assignment

Python assumes that a variable is local as soon as you assign it
a new value.
Don't flood the logs on every write
Be consistent
Add optional settings to example config

It took me a while to figure out I could set them :)
Merge pull request #3 from rubenk/master

Replace tags at config time instead of every write