Allow multiple builder instances

[felixge]

Right now the index.coffee exports only a single XMLBuilder instance.
This is problematic when building multiple XML's within a single node
process as it's essentially a singleton where none should be used.

This patch fixes it, but breaks API slightly.

[felixge]

Any chance of getting this merged?

[oozcitak]

Sorry for the delay. I understand the need for multiple builder instances. But I find the builder = require('xmlbuilder')() syntax a little confusing. Instead, I am thinking of adding a named export to return a new instance:

var xmlbuilder = require('xmlbuilder');
var xmldoc = xmlbuilder.create(); // Creates a new instance

[oozcitak]

Closed by 6828c05