process genome alignment in the Multiple Alignment Format

 MafFilter applies a series of "filters" to a MAF file, in order to
 clean it, extract data and computer statistics while keeping track of
 the associated meta-data such as genome coordinates and quality scores.
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  * It can process the alignment to remove low-quality / ambiguous /
    masked regions.
  * It can export data into a single or multiple alignment file in
    format such as Fasta or Clustal.
  * It can read annotation data in GFF or GTF format, and extract the
    corresponding alignment.
  * It can perform sliding windows calculations.
  * It can reconstruct phylogeny/genealogy along the genome alignment.
  * It can compute population genetics statistics, such as site
    frequency spectrum, number of fixed/polymorphic sites, etc.