Support for Encryption

[jaime-olivares]

I have started to work on encryption using modern AES128 and AES256 algorithm (as opposite to the original PKZIP algorithm).

Working on branch encrypt

Encryption will be enabled by calling ZipStorer.SetPassword(password) for the incoming ZipFileEntries. The password will be stored in a SecureString object.

Encryption will always use AES256 and decryption will support both AES128 and AES256.

Currently, I am trying to determine the right flags to be set in the local header and central dir.