Add Ekko / Sleep Obfuscation to Sliver

[armysick]

Card

This PR implements Ekko / in-memory sleep obfuscation for a beacon.

Details

Based on the work of https://github.com/scriptchildie/goEkko, adapted from https://github.com/Cracked5pider/Ekko, it pauses Go runtime and encrypts the beacon's memory region with the Ekko technique.

Command -B / --sleep-obfuscation added on generate beacon to support this feature.
Only applicable for Windows.

Beacon while performing operations / active:

Beacon while in its sleep duration:

[moloch--]

Looks awesome we'll try to get this reviewed and merged shortly!

[rkervella]

Couple of things to changes before I can dynamically test that one:

• please don't print to stdout when you're not in debug mode
• generate the XOR key dynamically at runtime instead of the hardcoded buffer of 0x55 values.

[armysick]

Heya, @rkervella !

Thanks for the first review. Cleaned out the prints and randomised XOR key generation.
Tested it again and looking through process hacker, functionality remains the same after the changes.