Modified CNV transition matrix and more:

- replaced -i with -x and added -P which allows to modify the prior
  of both samples being the same
- fixed a typo in cn4_baf, wrong peak was used
- minor updates in description strings in vcfmerge and polysomy
concat: Informative error msg for nonexistent -f files. Resolves #177
Minor fix in manpage: AC is the count, not number, of alternate alleles. Partially resolves #164