Update Integer, phase 1

[sampersand]

This updates Integer's signatures. Since Integer is such an important class, I've broken it up into multiple phases.

This first phase does two things:

1. Modernized the test suite for Integer_test.rb. Note that since not all methods were implemented, test methods for missing ones are no-ops.
2. Updated signatures for all non-complicated, non-coerce-reliant methods.