message: Update version macro to 0.15
  Also add a somewhat redundant comment that makes sure that grepping for
  0.15 finds all lines that need to be changed.
diff: #include <stddef.h>
  /* Version macro; major * 1000 + minor * 10 + patch */
  -#define MESHOPTIMIZER_VERSION 140
  +#define MESHOPTIMIZER_VERSION 150 /* 0.15 */
  /* If no API is defined, assume default */
  #ifndef MESHOPTIMIZER_API
  