Renamed error* to status* in C files which were left out of earlier commits.
Switched order of (length,array) arguments to (array,length).

* Also applies to C strings, e.g. 'status_message' now appears before
  'status_message_length'.
* Updated comments in concert.
Added reporting of optimization statistics.

* Statistics: number iterations, number function evaluations, number
  gradient evaluations.
* Number of evaluations returned from FORTRAN 77 L-BFGS-B actually means
  number of FG* tasks returned from L-BFGS-B.  Each FG* task results in
  both a function and a gradient evaluation so the total number of
  individual evaluations is actually double.
* Statistics returned individually in Fortran and C code rather than as
  a struct.
* Included statistics in example program.