Add a --skip-discardable flag to remove unusable rop gadgets from scrambled PE sections

[Acebond]

Hello,

ropr currently returns rop gadgets within DISCARDABLE sections of an executable file. This is generally fine as this flag/characteristics is ignore for userland binaries but when working with kernel mode drives/executables, such as with ntoskrnl.exe, the DISCARDABLE flag causes "the contents will be removed from memory after initialization is complete" (reference: https://devblogs.microsoft.com/oldnewthing/20120712-00/?p=7143).

For example, on ntoskrnl.exe, (see https://pedump.me/42a130909c358ce63f80c1a9dd0a061d/#pe), any section marked DISCARDABLE will be randomized every boot.

Proof:

It would be cool to have the option to exclude these sections from ropr output (with something like --skip-discardable) to prevent being polluted with unusable gadgets.

It should be fairly easy to identify sections marked DISCARDABLE as it will be in the section characteristics.