fakit v0.2.7 with faster speed and lower memory usage!

• _reduce memory usage_ by optimize the outputing of sequences.
  detail: using BufferedByteSliceWrapper to resuse bytes.Buffer.
• _reduce memory usage and improve speed_ by using custom buffered
  reading mechanism, instead of using standard library bufio,
  which is slow for large genome sequence.
• discard strategy of "buffer" and "chunk" of FASTA/Q records,
  just parse records one by one.
• delete global flags -c (--chunk-size) and -b (--buffer-size).
• add function testing scripts