- Remove useless operators
- Minor improvments in GreedyReduceVisitor

- Table name of QIRTable now a QIRNode
- Fix toString for QIRString

- Remove old hack in PostgreSQL driver
- Rename QIRSelect in QIRFilter to avoid confusions with SQL's select

- Minor fixes

- Better toString for QIRLambda
- Throw exception in case of error in execution of query

- Add getDriver for QIROperators

- DBDriver is now generic, rest merged with SQLDriver
- Add QIRException
- Use final everywhere it applies

- Fix QIRFreeVarsVisitor

- Add QIRFreeVarsVisitor to find the free variables in a QIR tree
- Add SQLDriver as abstract driver to factorize code between drivers for SQL
databases
- QIRVariable now contains a FrameSlot from Truffle
- QIRTable now contains a DBDriver to refer to a targeted database
- QIRReductor now returns a QIROperator

- Add naive QIR reduction

	- add basic PostgreSQL driver;
	- ConnectionData is now the same for all drivers
	- remove useless QIRDriver
	- minor changes in OracleDriver
- Cleanup in IQIRVisitor
- Minor changes

- Adds timeout to Oracle database connection