Properly handle using directives in scala-cli

[romanowski]

As for now, our integration with using directives is not perfect namely:

• we should properly handle directives other then string (numerical and binary) in all our process (probably enforce it within API somehow). Where it makes sense we should support it (e.g. numerical for Scala version) and where not we should fail with proper error message
• we should report proper errors for directives that does not parse (properly handle reporter from using direcectives)
• using directives should print proper positions