Move dummy_site fixture to conftest

This is eventually going to have many uses, so move it now and make
it generally available.
Add versioned options support to the Query command

- The Query class now takes an option_str argument to __init__
- All options are specified and versioned appropriately
- README updated to reflect this is complete
- Tests added to check the versioning support
- Example script updated for new signature of Query() class
- Exception documented for parsing options
- Query() class initialization documentation updated
Reinstate Python 3.3 as a tox environment

Not everyone will have upgraded to 3.4, so keep testing on 3.3 as
well.