Stub by address, not by function name

[erdnaxe]

When using Rainbow with multiple complex binaries loaded in memory, it is common to have multiple function with the same name.

This patch proposes to change how Rainbow internally handle stubbing:

• Before: user can only stub the first function matching the name given.
• After: user can stub all function matching the name given, or a function by its address.

This also increases reproducibility of experiments conducted using Rainbow.

Note
This creates a breaking changes as emu.stubbed_functions will now contain function addresses.