/**
 *   Plugin API:
 *   ----------
 *   const char *about(void)
 *      - short description used by 'bcftools plugin -lv'
 *
 *   const char *usage(void)
 *      - longer description used by 'bcftools +name -h'
 *
 *   int run(int argc, char **argv)
 *      - if implemented, the control is immediately handed over to the plugin,
 *      none of the init/process/destroy functions is called.  Return 0 on
 *      success or non-zero value on error.
 *
 *   int init(int argc, char **argv, bcf_hdr_t *in_hdr, bcf_hdr_t *out_hdr)
 *      - called once at startup, allows to initialize local variables.
 *      Return 1 to suppress normal VCF/BCF header output, -1 on critical
 *      errors, 0 otherwise.
 *
 *   bcf1_t *process(bcf1_t *rec)
 *      - called for each VCF record, return NULL for no output
 *
 *   void destroy(void)
 *      - called after all lines have been processed to clean up
 */