This tool can be used to sort a `fastx` file or
a pair of equivalently sized `fastx` files based on
sequence.
If an `R2` is provided, then the default is to sort
on its sequences.
``` bash
fxtools sort -i <your_file.fastq>
fxtools sort -i <your_R1.fq.gz> -I <your_R2.fq.gz>
fxtools sort -i <your_R1.fq.gz> -I <your_R2.fq.gz> --sort-by-r1
```