Merged pull request #276 from saimn/yum.

new yum plugin with useful aliases

plugins/yum/yum.plugin.zsh

+## Aliases
+
+alias ys="yum search"                       # search package
+alias yp="yum info"                         # show package info
+alias yl="yum list"                         # list packages
+alias yli="yum list installed"              # print all installed packages
+
+alias yu="sudo yum update"                  # upgrate packages
+alias yi="sudo yum install"                 # install package
+alias yr="sudo yum remove"                  # remove package
+alias yrl="sudo yum remove --remove-leaves" # remove package and leaves
+alias yc="sudo yum clean all"               # clean cache