Update OPAM setup

Recent OPAM versions generate more elaborate setup code.
Add homebrew-cask aliases to homebrew module

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Only print fortunes in terminals
Ignore case in filenames

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Try `lesspipe` in addition to `lesspipe.sh` for LESSOPEN

Debian based systems have `lesspipe`, without '.sh' suffix.
Since `$commands` is an associative array, we do index search and set
the input preprocessor on first match.