The recommended way to install tweeper globally is to install all its files
under /usr/share/php/tweeper and then make a symlink to the wrapper script
"tweeper" under /usr/bin

Tweeper depends on php-symfony-serializer which is used to convert json to xml
for some sites which provide the timeline data in json rather than in directly
transformable html.

NOTE: Tweeper also depends indirectly on php-symfony-property-access because
the code relies on the ObjectNormalizer class which requires the
PropertyAccess component, see
http://symfony.com/doc/current/components/serializer.html#installation