Add list of installed PHP version

[cbourgois]

It will be useful to have the list of PHP installed versions in this script

$ sphp
Usage: sphp [phpversion]
Installed versions:
php56
php70

Maybe by adding

brew list | grep '^php[0-9]\{2,\}$'

[rechl]

Hi cbourgois,

thank you very much for your proposal and pull request. I did not receive a notification about it :( But now i will have a look and merge if everything is ok.

Thanks for contributing!

[rechl]

feature is added