Go archive/zip plus encryption support

This is a fork of the archive/zip package from the Go standard library which adds support for both the legacy (insecure) ZIP encryption scheme and for newer AES-based encryption schemes introduced with WinZip. It is based on Go 1.14.

This is based on work by Alex Mullins and Yakub Kristianto. The forward-port was done to introduce bugfixes and enhancements, such as missing support for large (>= 4GB) ZIP files like those distributed by VirusShare.