Improve backtracking call to append/3.

Thanks pmoura for the suggestion!
If `~/.bash_profile` doesn't exist, look for `~/.profile` for setting the path to the `marelle` command

This is necessary for users define their environment using `~/.profile` instead of `~/.bash_profile` as creating from scratch a `~/.bash_profile` file will override the user `~/.profile`.
Minor indent cleanup.
Update apt/brew during bootstrap.
Rewrite `main/1` into `main/2` to take advantage of Prolog first-argument indexing
Fix typo in arg handling.
Merge branch 'master' of https://github.com/larsyencken/marelle into upstream