Added support for regex ignores

> LBo: I just looked at the sitemap extension
> LBo: Is it true that you can't ignore entry pages at the moment?
> LBo: I have for example /blogs but I don't have /blogs/blog1
> LBo: But the sitemap extension generates a url for each blog item
> LBo: What would be a good way to make the sitemap ignore those?
> LBo: I thought about extending the 'ignore' yml config option with a glob or regex
> Bopp: hi, lbo
> LBo: So you could do something like ignore: [ '/blogs/*']
> Bopp: Sounds good to me.
> LBo: A preference for globs or regex?
> Bopp: regex :-)
> LBo: Ok, great

I tried creating a unit test but I didn't know how to create the tests structure for an extension and I couldn't find an example. I wanted to test it like this:

``` php
    public function testIgnoreLinks()
    {
        $tests = array(
            array(
                'link' => '/',
                'ignore' => '',
                'ignored' => false,
            ),
            array(
                'link' => '/',
                'ignore' => '/',
                'ignored' => true,
            ),
            array(
                'link' => '/pages',
                'ignore' => '/',
                'ignored' => false,
            ),
            array(
                'link' => '/pages',
                'ignore' => '/pages',
                'ignored' => true,
            ),
            array(
                'link' => '/pages',
                'ignore' => '/pages/',
                'ignored' => false,
            ),
            array(
                'link' => '/pages/test-1',
                'ignore' => '/pages/',
                'ignored' => false,
            ),
            array(
                'link' => '/pages/test-1',
                'ignore' => '/pages/.*',
                'ignored' => true,
            ),
            array(
                'link' => '/pages/test-1',
                'ignore' => '/pages/\.*',
                'ignored' => false,
            ),
            array(
                'link' => '/pages/test-1',
                'ignore' => '/pages/test-[2-9]*',
                'ignored' => false,
            ),
            array(
                'link' => '/pages/test-1',
                'ignore' => '/pages/test-[1-9]*',
                'ignored' => true,
            ),
        );

        foreach ($tests as $test) {
            $this->config = array(
                'ignore' => array($test['ignore'])
            );

            $this->assertSame($this->linkIsIgnored($test), $test['ignored']);
        }
    }
```