Function: contfraceval
Section: sums
C-Name: contfraceval
Prototype: GGD-1,L,
Help: contfraceval(CF,t,{lim=-1}): given a continued fraction CF from
 contfracinit, evaluate the first lim terms of the continued fraction at t
 (all terms if lim is negative or omitted).
Doc: Given a continued fraction \kbd{CF} output by \kbd{contfracinit}, evaluate
 the first \kbd{lim} terms of the continued fraction at \kbd{t} (all
 terms if \kbd{lim} is negative or omitted; if positive, \kbd{lim} must be
 less than or equal to the length of \kbd{CF}.
