Emit base options for Integer()

[dgollahon]

Simply forcing the use of Integer is actually kind of misleading/dangerous. Our goal with mutest should be to help people write correct software that is free of bugs but, while this is stricter than to_i in many ways, it has the surprising behavior of interpreting leading base information (ex: Integer('077') is not 77 since the 0 is interpreted as meaning 'octal').

See: mbj/mutant#704