Merge latest version of numerics.{h,cpp} into FlexibleSUSY.
This fixes a numeric non-continuity in the b22 function, which
can be seen from the following test program:

void compare(double m2)
{
   const double q = 91.0; // ren. scale
   const double p = 80.17362395461014;
   const double m1 = 762.7319319393943;

   setmudim(q*q);
   const double b00_looptools = Re(B00(p*p, m1*m1, m2*m2));

   const double b00_softsusy = b22(p, m1, m2, q);

   cout << "b00_looptools = " << b00_looptools << '\n'
        << "b00_softsusy  = " << b00_softsusy  << endl;

}

int main()
{
   ltini();

   compare(766.9340);
   compare(766.93403); // here Softsusy and LoopTools differ
                       // dramatically

   ltexi();

   return 0;
}