Better errors for database query style issues

[davenquinn]

This module allows mixing three different styles of query formatting:

1. SQLAlchemy-style high-level parameter binding
2. Psycopg2 parameter/identifier binding
3. DBAPI binding and adaptors

More may be added in the future, e.g., for support of SQLite with similar semantics to Psycopg2

Styles 2 and 3 allow both parameter and identifier binding, but with different semantics. We should make an attempt to inform the user when they are misusing these overlapping features with meaningful error messages.