Build a random part of the sequence orders in a FASTA formatted file. The random seed is fixed so the same part will be released in every circle of the program unless it is set.
Takes a FASTA file and the count of sequence orders to randomly opt .
Writes a FASTA patterned file to standard out having the defined subsample of the genuine file. If -rest is defined then any left over sequence orders are written to, which is efficient for cross-validation.