Implement new codegangsta/cli lib

This is a work in progress for #56, #28, #69 

Things:
- [x] add codegangsta/cli
- [x] update commands.go
- [x] ensure flags are parsed
- [x] ensure validation is correct
- [x] handle errors
- [x] adds environment variables for flags
- [x] replace all usage instructions with: https://github.com/codegangsta/cli/blob/master/help.go#L117