improve unicode handling

Without this there can be times when the id is not correct encoding
and whoosh will throw an exception.
Add "tag" as a field alias for "tags".

This is just for convenience and to allow parity with the
tag search in the sqlalchemy based stores.
Some mild syntax adjustments for modern Python

This was going to be an exploration of making twp.whoosher 3.x
compatible, but there are issues in twp.utils that need to get fixed.
release 0.9.26

* add tag alias to tags