added the use of url encoded chars in username and password

By not using the '--user' commandline feature in curl but adding the username:password to the url it's possible to use for instance a 'colon' : within the username or a @.

If your username is "test:321" and password "pass" you can now use "test%3A321" as username parameter.
Now the login will not fail by thinking your username is "test" and your password "321pass" like in the current version of git-ftp.