Added directory independency support

With these changes, the Minotar package can somewhere other than the root of the web server. This is useful for people are fork the package for use on a server that serves more than one purpose.

Before, a lot of the code assumes that this package runs on the root of the server: klein respond functions are relative to server root, *not* the package's root, and a great deal of links, css, and internal calls to the exposed API are either relative to server root or point to the production site.