Added comment to extract.conf noting the use of an internal plugin for Hilink encrypted firmware extraction.

Fixed extraction bugs when recursively extracting multiple files at once; added some extraction API methods.

GUIDs coming from https://github.com/LongSoft/UEFITool/blob/new_engine/common/ffs.h

Invalidate capsules with unrealistic sizes, but would be better to check
against the remaining data length.

This should avoid reporting a number of false positives on UEFI PI headers,
and includes a list of known filesystems based on
https://github.com/LongSoft/UEFITool/blob/new_engine/common/ffs.h

The _FVH header is the actual fixed header, the GUID identifies the type of
filesystem instead. Since this seems to be the only known GUID valid for
this structure, accept it by itself, and report the size of the volume and
header.

Identify the GUIDs for EFI Capsule formats, both v0.9, v2 and UEFI
versions, which are essentially the same for what gets reported.