This commit adds these modifiers:
1. skipUpdates (with unit tests)
2. skipInserts (with unit tests)
3. skipQueries (no tests yet) (and not really working yet)
And handles two situations previously not considered:
1. Updates with no attributes will now return a properly formatted
error instead of returning a syntax error.
2. Inserts with no values will now work on SQLite, Postgres and
SQLServer
Vinícius Garcia