feature: adding support to parse/handle .sfx files that contain .7z data/files

[philsmd]

This topic was sometimes ask on hashcat forum and also recently discussed on jtr-jumbo github issues (openwall/john#2120).

The idea is to just "extract" the .7z from the .sfx automatically and parse it as if it was just a regular .7z file.

This feature should only support regular .sfx files (e.g. those generated by the 7-Zip tool itself). Packed executables won't be supported since they kinda need to be "executed"/analysed/unpacked first (that's a too advanced/rare format).

Thanks