Argument parsing corrections

[Shershebnev]

1. Several arguments were incorrectly converted to integer instead of float
   which rounded them. Arguments (like minhetfreq) that were in range (0, 1) were
   rounded to 0 and hence always assigned default values during later checks
   (BS-SNPer.pl:48-55 @ master)
2. It wasn't possible to set any argument to 0 as in this case in later checks
   (BS-SNPer.pl:48-55 @ master) 0 was interpreted as False and the default value
   was used in such cases.
3. It doesn't make sense to check @argv == 0 at line 47 as it will be empty
   after GetOptions. What makes sense is checking for files, as there are no
   default values for them. Although for output files it might be good idea
   to just construct them based on input filename by adding predefined suffixes,
   i.e. if $bam == file.bam, $methcg would be file.bam.methcg