Yandex Turbopages + tabs

[Rainbow-Spike]

1. Tabulations
2. Compatibility with requirements of Yandex Turbopages mobile service https://tech.yandex.com/turbo/
   New strings ## 41, 131-133, 139-140

My case https://comicslate.org/feed.php?onlynewpages=1
It has no errors in their feed debug tool http://screenshot.ru/6becfb15bd89f75d21395112dd297af7.png

[flack]

Hello & thanks for the PR!

Some notes:

• Is there really anything gained from changing all the whitespace in the file? The actual change is just those 6 lines: https://github.com/flack/UniversalFeedCreator/pull/10/files?w=1

If anything wrt to whitespace is changed, it should probably be done globally in the entire project, not just in one file

• right now the Yandex data gets added unconditionally, i.e. every user of this class will add the Yandex attributes, even if they never use it. Wouldn't it be better to make this configurable (e.g. by having a method enableYandexTurbo() or similar)?

• it has been a while since I've looked at the turbo stuff, but if I remember correctly, bot all tags are allowed inside of <turbo:content>. So shouldn't there be a way for users to set a different value for <turbo:content> and <description>?

[Rainbow-Spike]

• I'm a stranger here, so if spaces are not pleasing, I do not mind. I have already listed the useful string numbers - ## 41, 131-133, 139-140
• the idea of a switch for Yandex sounds as good, as idea about a difference in content customization too
• I inserted "…" as a substitute for the error presented by Yandex - the content inside CDATA-tag should not be empty

so you feel free to close this pull and make you vision