Merge pull request #1336 from aelesbao/plugin-systemd

systemd plugin

plugins/systemd/systemd.plugin.zsh

+user_commands=(
+  list-units is-active status show help list-unit-files
+  is-enabled list-jobs show-environment)
+
+sudo_commands=(
+  start stop reload restart try-restart isolate kill
+  reset-failed enable disable reenable preset mask unmask
+  link load cancel set-environment unset-environment)
+
+for c in $user_commands; do; alias sc-$c="systemctl $c"; done
+for c in $sudo_commands; do; alias sc-$c="sudo systemctl $c"; done