Basic Likelihood as a function of alpha (Salpeter)

- Implemented brute force calculation of alpha for an array
  of different alpha values.
- When Sum_K for a given i is 0.0, p_i = 0 so ln p_i = -inf,
  in these cases, assign ln p_i = -1000., but maybe a lower
  value is better.
- Currently, running best-alpha estimator on all "stars", will
  try next by making a cut around the MS only, by eye (including
  only rmag < R_90, i.e. where completeness function, which has
  not been implemented yet, can be ignored.