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

NOTES FOR PACKAGERS

Even though the php json extensions are used, namely json_decode(), a direct
dependency on php-json is not usually strictly necessary, because (at least on
Debian) php-cli already depends on it.

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.

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
