TorneLIB is able to handle plugins by the "pluggable" class and some libraries, primary such libraries we need to use ourselves, are linked in the main library. For example, a default template handler (Smarty) and JPGraph are currently supported by TorneLIB). To not mix up files and libraries, the pluggables are configurable through tornevall_config.json that is normally put into /etc (You might want to take a look on the example config file tornevall_config.sample.json).
Pluggable libraries path are set up in the PluggableAutoPath variable and the default is pointed to /usr/local/TorneLIB-Libraries. To install such supported library, for example JPGraph, download the library from http://jpgraph.net/download/ and then extract the archive and put it in this path. Just make sure that you are removing the current version number of JPGraph, as the pluggable will look for PluggableAutoPath/jpgraph.