Added family cumulant funcs and 2 dervs in c.

 Checked. To be implemented.
Moved cumulant and derivs to C.
Started moving el to C.
functions in c: cumulant, el (log data density).

Cumulant and log data density (el) each have two derivatives also written in C. Functions have been written in C, are implemented in PQL and objfun (called by glmm), and tested. A couple additional helper functions written in C (to perform matrix multiplication etc).