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
The example you are mentioning is equivalent to `node-debug app --debug-mode`, right? So a developer can write a simple script to achieve the same result: 

```
#!/bin/sh
node-debug app --debug-mode
```

This is IMO more flexible, as you can have several such scripts, while there is only single rc file.

> The second reason to add this option - avoid argv parsing outside of `config.js`

I don't understand how these two are related, considering that the argv-based approach of passing the parameters to the debugged process is still supported.

I agree it's best to keep all argv parsing code inside `config.js`. Can you keep the parsing code in config.js and do not expose `script` option to the users at the same time?

> It's not an important feature, I can exclude it, if you want.

Yes please, exclude it. The less features we are, the less time we have to spend on maintenance and support.