1) move test and benchmark function from gfa.R to test.R
2) add .logC.coef, compute log(N choose i) for i=1,...N
3) add gfit.bezier.part, a inhanced gift.bezier:
    use argument 'time' ---- control sample frame, maintain default behavior
    use argument 'res' to control resoluction of fitted function
    use argument 'part' to partition coneficient matrix to cope of memory problem