npm init - add interactive, or command line options (#357)

There were a lot of things wrong with `npm create` in the prior version.
But I didn't know this, because `npm create` doesn't work against a
local package, much as that is sometimes claimed.

Fixes:
*If no command line arguments, do interactive
*If command line arguments, do what they say
*If extraneous options, because the user didn't realize `npm create`
butchers your command unless you put `--`, throw an error.