Add a basic chunk plugin

It'd be useful to have a plugin that splits a long text into a series of smaller ones (e.g. sentences, paragraphs...). Ideally, it would take a delimiter or similar argument.

It should be trivial to implement this plugin. The only complication would be handling the id of the pieces, since they should follow one of NIF schemes.

Once implemented, it could be used like this: http://localhost:5000/api?i=hello there&algorithm=split,rand.