New aliases for repo plugin

This helps a lot in day to day android development:
- rs: repo sync (git fetch on all projects)
- rra: auto rebase for all projet without loosing uncommited changes
- rsrra: do both steps at once
Signed-off-by: Gaetan Semet <gaetan@xeberon.net>

plugins/repo/repo.plugin.zsh

 # Aliases
 alias r='repo'
+compdef _repo r=repo
+
+alias rra='repo rebase --auto-stash'
+compdef _repo rra='repo rebase --auto-stash'
+
+alias rs='repo sync'
+compdef _repo rs='repo sync'
+
+alias rsrra='repo sync ; repo rebase --auto-stash'
+compdef _repo rsrra='repo sync ; repo rebase --auto-stash'