Adding support for additional query languages

Each Quepy application can define its own query output language by
including a printout.py file and an appropriately named
expression_to_myquerylang function. When generating a query you can now
pass a query_lang='myquerylang' parameter. The query language defaults
to SPARQL if no query_lang is specified.

See freebase-quepy for an example of adding a new query language (MQL): https://github.com/narphorium/quepy-freebase