1 - re-evaluate the use of trigger_error() or use a custom error handler,
2 because right now the code exists as soon as trigger_error() gets called and
3 any following code is ignored.
5 - write better XSL stylesheets? I am not an XSL expert
6 - evaluate the use of the <ttl/> RSS element
7 - show cards directly in RSS items for twitter.com
8 - show direct links for videos in the Instagram feed
9 - check the encoding of the tweets when UTF is used,
10 maybe solvable with mb_convert_encoding()?
11 See http://php.net/manual/en/domdocument.loadhtml.php
13 - The dependencies on the symphony components in composer.json could be more
14 relaxed like ">=2.7.0", but for now sticking to "2.7.*" is good enough.