[patch] Add user access permissions feature to encrypt method

[KLEIN Stéphane]

Hi,

I've write a patch to add user access permissions feature to encrypt method.

Now, encrypt method PdfFileWriter class has "user_access_permissions" parameter.

Example to use :

>>> from pyPdf import PdfFileWriter, PdfFileReader, UserAccessPermissions
>>> output = PdfFileWriter()
>>> output.encrypt(
... user_pwd = "",
... owner_pwd = "password2",
... user_access_permissions = UserAccessPermissions.print_document | UserAccessPermissions.content_copying_for_accessibility
... )