Vim: `ag` for CtrlP.

Thanks thoughtbot & gsamokovarov.
Scripts: Extend `search`.

Use extended regular expressions syntax for Grep.
Set 'pipefail' so we exit with a non-zero code if Grep fails.
Bail early if we know Grep will fail, e.g., directory not found.
Scripts: Print basename only in `unpack` error messages.

We are no longer in a function so use 'exit' over 'return', you silly!
Vim: Airline theme patch, again.
Scripts: Teach `unpack` about *.sfx and *.rar files.
Aliases: More Ubuntu-specific stuff.