Add the option to ask interactively for the username.

Add the option to ask interactively for the username to make it easier to
share a config file between multiple users.

The read_password function is changed to read_input and supports reading the
pressed keys and displaying them (normal input) or displaying "*" (password).

Signed-off-by: Gert Hulselmans <hulselmansgert@gmail.com>
Merge pull request #11 from ghuls/ask_username

Add the option to ask interactively for the username.