Adding a hiding option to \cli\prompt

I was trying to create a prompt for passwords, and those are the changes I needed.

Sorry if the code style is not what you're used to, but honestly I found the original style quite confusing, so I did my best.

I tested it using PuTTY and noticed some weird behaviour, like in the screenshot below, but it looks more like a bug in the program, since after a clear it does not happen.

![capture](https://f.cloud.github.com/assets/532299/1641273/a48eb67a-584f-11e3-880d-0289ce903249.JPG)