Added command line functionality among other minor changes

I have added command line functionality to passwordstrength. The user can install the script using the provided setup.py file (`# python setup.py install`) and they should then be able to invoke `passwordstrength` in a terminal to test the strength of these passwords. An example of such behaviour is below:

`
$ passwordstrength
Password: [password input obfuscated using getpass]
Score: 59
$ # alternatively...
$ passwordstrength -r
Password: [password input obfuscated using getpass]
Score: 59
OK
$ ...
`

I have also fixed a bug in the method `get_readable_score()`. This bug would cause the lowest possible readable score to be given for any inputted password, even if it were extremely strong. This function now checks ranges by making use of the `x in range(n1, n2)` conditional expression.

Finally, I have fixed a few typos in the code. :)