Function: fromdigits
Section: conversions
C-Name: fromdigits
Prototype: GDG
Help: fromdigits(x,{b=10}): gives the integer formed by the elements of x seen
 as the digits of a number in base b.
Doc: gives the integer formed by the elements of $x$ seen as the digits of a
 number in base $b$ ($b = 10$ by default).  This is the reverse of \kbd{digits}:
 \bprog
 ? digits(1234,5)
 %1 = [1,4,4,1,4]
 ? fromdigits([1,4,4,1,4],5)
 %2 = 1234
 @eprog\noindent By convention, $0$ has no digits:
 \bprog
 ? fromdigits([])
 %3 = 0
 @eprog
