Operands and operators should be pythonic

Operations should expose a more pythonic API, to make things more pleasant when handling the operands directly. To build an equality operation, for example, one must do `Equal(operand1, operand2)` -- `operand1 == operand2` doesn't work. As a consequence, Booleano operands must implement the so-called "rich comparison methods" so these expressions can be used (e.g., `operand1 == operand2` will be transformed under-the-hood into `Equal(operand1, operand2)`). All the operators must be implemented, unless there's no Python equivalent.