Templated functions

[richfitz]

Allow creation of functions that create or use (or both) templated types. This used to work but I got rid of it, and now I need it back. There are still bits for the tests within the template example package.

[richfitz]

Basically done, but needs roxygen support.

[richfitz]

Also needs support for manual class lists (turns up in traitecoevo/plant: plant_to_plant_plus).