add declarations for net.isIP*

[rsolomo]

No description provided.

[gabelevi]

Should the input type be string? The d.ts seems to use string, and the spec is somewhat unclear

[rsolomo]

I would lean towards any since the doc seems to be unclear if the input must be a string, and any would more closely match the signature of other is* functions.

Also, it's not mentioned in the documentation, but it may (or may not) be worth noting the function does have the behaivor of casting the input argument to a string.
In other words this prints true, even though the argument is not a string:

var net = require('net')
var x = {
  toString: function() {
    return '127.0.0.1'
  }
}

console.log(net.isIPv4(x)) // true

[gabelevi]

If these functions are implicitly cast to strings, then I would recommend making the parameter type string. This means the user of the function would have to explicitly cast the argument to string before calling the function, like net.isIPv4(String(x)). My intuition is telling me

1. I'd guess that it's somewhat rare to pass stringable objects to these APIs
2. I'd guess actually type errors like passing null or undefined to these functions are somewhat common
3. The workaround (casting to String) is easy enough that even if people do use stringable objects they're not terribly inconvenienced

That being said, I don't feel terribly strongly here. If you still disagree let me know and I'll merge your PR :)

[rsolomo]

Okay, that's fine. String it is.