Issue 83 - Add scriptcs.opts for command line options

- Initial stuff
- Config file holds only scriptcs.exe arguments (everything before --)

Up for discussion:
- I've moved ArgumentParser into CompositionRoot - I think it look nicer from the Program.Main point of view, but still continue FileSystem hack.
- I want to load config, then overload it with command line arguments - although I don't want to rewrite Args.Parse. My approach is to parse cmd args and config file separately produce two ScriptCsArgs and then merge it into one. Problem I'm having is with default values, e.g.. user defines debug: true in config file and then explicitly states -debug false in command line. The correct result should be false but my current algorithm will result in true. It's because I have no way of knowing if the the value is explicitly defined (false) or it's default (also false) well at least not without looking up args array - which I would like to avoid. Any thoughts?