Per the error message:
```
$ bubu
...
Warning: brew upgrade with no arguments will change behaviour soon!
It currently upgrades all formula but this will soon change to require '--all'.
Please update any workflows, documentation and scripts!
```
Merge completion with official brew completion. Add a helper to link official
completion into oh-my-zsh plugin (without overwriting). Add an alias to list
installed brews. Add brews to the path (in a somewhat strange way).
