stats: Compute checksum for names/seqs/quals
fix DPR annotation

* Max alleles got changed in 8030ea3 to 5 instead of 4 to
  fix a speparate bug, but 4 left at line 127 in bam2bcf.c
  when initialising memory. This leads to bug reported in
  #274
* Fix this, but also make `B2B_MAX_ALLELES' a constant to
  set this number everywhere it is used (@pd3 please check)
* Parsing of tags was broken. the `--tag' options in the
  example in #274 should not have been parsed. Should be
  fixed now
* Add test output for all `--tags' options

Fixes #274
No need to initialise array anyway
Merge stats checksums