sitemap.xml: reduce a number of spaces

[php-coder]

At this moment, sitemap.xml is optimized for human readability but it contains a lot of spaces that we can remove in order to make a file smaller.

So, instead of

<url>
        <loc>https://my-stamps.ru/series/6</loc>
        <lastmod>2014-02-12T00:08+04:00</lastmod>
</url>
<url>
        <loc>https://my-stamps.ru/series/7</loc>
        <lastmod>2017-11-08T00:27+03:00</lastmod>
</url>

we can write it like this:

<url><loc>https://my-stamps.ru/series/6</loc><lastmod>2014-02-12T00:08+04:00</lastmod></url>
<url><loc>https://my-stamps.ru/series/7</loc><lastmod>2017-11-08T00:27+03:00</lastmod></url>

It still readable but more compact.

Another idea is to remove an indentation before <url>.

[php-coder]

I tried to benchmark it but it shows only the speed of my internet access:

$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	96253
Total time:	0,561072
Download speed:	171551,000
$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	96253
Total time:	0,546817
Download speed:	176024,000
$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	96253
Total time:	0,587232
Download speed:	163909,000

After:

$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	87922
Total time:	0,632111
Download speed:	139092,000
$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	87922
Total time:	0,590992
Download speed:	148770,000
$ curl -s -S 'https://my-stamps.ru/sitemap.xml' -w 'Document size:\t%{size_download}\nTotal time:\t%{time_total}\nDownload speed:\t%{speed_download}\n' -o /dev/null
Document size:	87922
Total time:	0,598708
Download speed:	146852,000

The size of document decreased for sure.