play well with github/nginx.
Introduces a breaking constructing change, there is now a 'callback url' argument that can be supplied prior to the signatureMethod in the constructor. Pass 'null' to explicitly ensure the callback url is never used, 'undefined' to use 'oob', 'oob' to use 'oob' or an absolute url.
…o path given the normalised url has a trailing slash)
…s (POST stylee) works.