Restructured configuration system

Configuration logic from node-debug.js moved to config.js
node-debug receive configuration from rc now
config uses yargs argv preprocessor now
Removed conversion part of config.js
Fixed hight priority of node-debug hardcoded defaults
Fixed default web host for node-debug
  (`127.0.0.1` instead of `localhost`)
Fixed null value of web host
  (default web host is empty string now)
Added script option
Added list of avaible options as default help info
As long as the user does not have an easy way how to pass `''` value for `--web-host`, your proposed solution is ok.

You know what? Let's stick to what you proposed, we can always implement more cases later, when somebody asks for it.

I.e. `inspectorHost == '0.0.0.0' ? '127.0.0.1' : inspectorHost;` is fine.