FUNCTION:  RootCoords - coordinates of a vector w.r.t. simple roots,    
CALLING SEQUENCE:  RootCoords(v,R);,    
PARAMETERS:  R = a root system data Structure
             v = a linear combination of e1,e2,...,SYNOPSIS:   
  A "vector" (distinct from the vector data Structure used by Maple) is a
  linear combination of the standard orthonormal basis e1,e2,e3,..., with
  coefficients that are rational or floating-point.
  If v is a vector in the span of Base(R), RootCoords(v,R) returns
  the list of coordinates of v relative to the simple roots in Base(R).,   
  that the function calls coeff(v,e1),coeff(v,e2),... return valid answers.
  That is, the coefficients of v need not be rational or floating-point.

  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   
  RootCoords(HighestRoot(G2),G2);      yields           [3,2]
  RootCoords(a*e1+b*e2+c*e3,B3);        yields      [a+b+c, b+c, c]
  RootCoords(2*e2,H3);                  yields
  evalf(",3);                                       [2.62, 3.24, 1.62],    
