Ported pacman aliases from oh-my-zsh's archlinux plugin.

Added support for having multiple sub-plugins within the archlinux family.
Fixed incorrect plugin name
Removed command; it's not necessary.
Fixed typo
Ported function to zsh
Added description
Ported function to zsh
Ported function to zsh
Fixed Indentation problem
Removed unnecessary sudo
Corrected logic when testing if  exists.
Merge pull request #122 from skk/archlinux