Added header decorators support to allow adding custom headers.
Example:

soap.createClient(url, {}, function(err, client) {

        // tune the client to allow adding more headers, since the original doesn't support it

        client.addHeaderDecorator(function(headers, method, args, location) {
            headers['heade-key'] = 'header value;
        });
reverted back to original
Fixed the issue that cases empty value when a parameter value is 0 or false
Merge pull request #2 from dimichgh/master

Merge with dimichghs fix