Function to add a new default package parameters. Mostly used
to add a new texture triangle definition.
TT.add(..., par.list = "TT.par", bkp.par.list = "TT.par.bkp",
par.env = TT.env)
Julien Moeys [aut, cre], Wei Shangguan [ctb], Rainer Petzold [ctb], Budiman Minasny [ctb], Bogdan Rosca [ctb], Nic Jelinski [ctb], Wiktor Zelazny [ctb], Rodolfo Marcondes Silva Souza [ctb], Jose Lucas Safanelli [ctb], Alexandre ten Caten [ctb]