Interleaved fastq file

[lskatz]

I think related to #3 (?), how would you parse an interleaved fastq file? Where read 1 is the first entry of the file and read 2 is the second entry, etc. Thank you!

[lskatz]

Here is how I hacked it but I would love to use the parallel.each function instead. https://github.com/lskatz/fasten/blob/fast-fastq-parser/src/bin/fasten_combine.rs#L51 and on the same script, https://github.com/lskatz/fasten/blob/fast-fastq-parser/src/bin/fasten_combine.rs#L83 (I am also seeing a bug where I need to put that code on line 83 down to the bottom of the loop)