pr12 (one task)
helpers.read_file: return '' if no file
helpers.new_fasta: result has method :add_seq
helpers.is_palindrome
pr12.find-orfs-in-frame: fix errors
pr12.find-fixed-palindromes
pr11.filter-palindromes: fix possible empty seqs
pr12.filter-palindromes
count-stop-codones
pr12.filter-orfs
pr12.dna-consensus
pr12.protein-consensus
pr12.reorigin
pr12.translation-cmp
pr12.find-matrix
pr12.translate-orf
pr12.untranslate
pr12.find-substrings
pr12.find-repeats
pr12.filter-non-polar