FUNCTION: LieTools/SymMap
USAGE: SymMap(gpoly);
SYNOPSIS: SymMap is the symmetrizer map from S[g] -> U[g]
EXAMPLE: 
> SymMap(g[1]*g[2]*g[3]);

  1/6 u(g[1], g[2], g[3]) + 1/6 u(g[1], g[3], g[2])

         + 1/6 u(g[2], g[1], g[3]) + 1/6 u(g[2], g[3], g[1])

         + 1/6 u(g[3], g[1], g[2]) + 1/6 u(g[3], g[2], g[1])

SEE ALSO: LieTools[InvSymMap], LieTools[NormalOrder]
