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
Please extract a generic method `filterOptions` and use it in other `filter*` methods.

```js
Config.filterOptions = function(options, filterFn) {
  var filteredOptions = {};

  Object.keys(options).forEach(function(key) {
    var dashedKey = keyToDashedKey(key);
    var definition = definitions[dashedKey];

    if (filterFn(definition)) {
      filteredOptions[key] = options[key];
  });

  return filteredOptions;
};

Config.filterDefaultValues = function(options) {
  Config.filterOptions(options, function(definition) {
    return !definition || definition && definition.default !== options[key]
  });
};

//etc.
```

The name `filterOptions` may not be the best one, feel free to come up with a better one.