anchor.diff:  ----
   double *inform_local_block_entropy(int const *series, size_t n,
           size_t m, int b, size_t k, double *ent, inform_error *err);
  +----
  +Compute the local block entropy of a time series with block size `k`.
  +
  +*Examples:*
  +
  +One initial condition:
  +[source,c]
  +----
  +inform_error err = INFORM_SUCCESS;
  +int const series[9] = {0,0,1,1,1,1,0,0,0};
  +
  +// k == 1
  +double *h = inform_local_block_entropy(series, 1, 9, 2, 1, NULL, &err);
  +assert(inform_succeeded(&err));
  +// h ~ { 0.848, 0.848, 1.170, 1.170, 1.170, 1.170, 0.848, 0.848, 0.848 }
  +
  +// k == 2
  +double *h = inform_local_block_entropy(series, 1, 9, 2, 2, NULL, &err);
  +assert(inform_succeeded(&err));
  +// h ~ { 1.415, 3.000, 1.415, 1.415, 1.415, 3.000, 1.415, 1.415 }
  +
  +free(ai);
  +----
  +
  +Two initial conditions:
  +[source,c]
  +----
  +inform_error err = INFORM_SUCCESS;
  +int const series[18] = {0,0,1,1,1,1,0,0,0,
  +                        1,0,0,1,0,0,1,0,0};
  +double h[16];
  +inform_local_block_entropy(series, 2, 9, 2, 2, h, &err);
  +assert(inform_succeeded(&err));
  +// h ~ { 1.415, 2.415, 2.415, 2.415, 2.415, 2.000, 1.415, 1.415,
  +//       2.000, 1.415, 2.415, 2.000, 1.415, 2.415, 2.000, 1.415 }
  +
  +// no need to free since `h` was statically allocated in this scope
  +// free(h);
   ----
   ****
   
  
positive.code: int const series[18] = {0,0,1,1,1,1,0,0,0,
                          1,0,0,1,0,0,1,0,0};
  double ai[14];
  inform_local_active_info(series, 1, 9, 2, 2, ai, &err);
  assert(inform_succeeded(&err));
  // ai ~ { 0.807, -0.363, 0.637, 0.637, -0.778, 0.807, -1.193,
  //        0.807,  0.807, 0.222, 0.807,  0.807, 0.222,  0.807 }
  
negative.code: 
  [[block-entropy]]
  == Block Entropy
  Block entropy, also known as stem:[N]-gram entropy <<Shannon1948>>, is the standard Shannon
  entropy of the stem:[k]-histories of a time series:
  [stem]
  ++++
  H(X^{(k)}) = -\sum_{x_i^{(k)}} p(x_i^{(k)}) \log_2{p(x_i^{(k)})}
  ++++
  which reduces to the traditional Shannon entropy for stem:[k=1].
  
  ****
  [[inform_block_entropy]]
  