Cleanse arborescence

Hi @jzellner,
Nice work! Thank you for putting it out there.

Here are a few corrections, more relative to the form than the content of your library.

Note that I added a "press q to quit demo" feature. It however leaves the terminal window in shambles sometimes.
Could you [take a look at it](https://github.com/fenollp/encurses/blob/757bc043fd36e2cf5f0dd9c914ddfb8b518423c1/src/encurses_demo.erl#L141)? I think I am using your code to close the demo…