New port: shells/zsh-antigen

Antigen is a small set of functions that help you easily manage
your Z shell (zsh) plugins, called bundles. The concept is pretty
much the same as bundles in a typical vim+pathogen setup. Antigen
is to zsh, what Vundle is to vim.

WWW: https://github.com/zsh-users/antigen

PR: 217706
Submitted by: Victor <gudfitz@gmail.com>