inline T manhattan_distance()

in src/annoylib.h [184:189]

• 6 lines of code
• 2 McCabe index (conditional complexity)

inline T manhattan_distance(const T* x, const T* y, int f) {
  T d = 0.0;
  for (int i = 0; i < f; i++)
    d += fabs(x[i] - y[i]);
  return d;
}