Allow hiding password length

[szh]

Addresses comments to #386

This PR allows you to set the HideCharacter to a space which will be interpreted by the RuneReader to mean that the user input should not be echoed and that it shouldn't print a "mask" either.

[AlecAivazis]

This looks good - mind adding a test case to this file?

[szh]

This looks good - mind adding a test case to this file?

I don't see how to add a test case there since the prompt is the same. I think this would require some refactoring. Do you want me to attempt?

[szh]

@AlecAivazis can we get this moving?

[AlecAivazis]

Yea feel free to refactor the tests to verify this behavior

[AlecAivazis]

Whoops! Wrong button 😅