Added support for subsites and index page

[TheMaaarc]

This fix solves the Problems from Issue #7.

Pico Version: 0.8

[ahi]

In my case, $file_url is something like http://localhost:8080/sub/page.
Replacing this:

if($file_url == "/") {
    $file_url = 'index';
}

with this:

$file_url = parse_url($file_url, PHP_URL_PATH);
if (substr($file_url, -1) == '/') {
    $file_url .= 'index';
}

fixed the problem.