add support for multiple input files

[tolot27]

This PR adds support for multiple input files and can be a workaround for #6.

[splaisan]

I am trying to achieve this as ONT generagtes multiple fastq files, can yuo please indicate how we can launch filtlong with multiple inputs, I tried fastq_pass/*.fastq.gz and <(zcat fastq_pass/*.fastq.gz) as last argument and they both did only one pass and died.
My only workaround is to zcat the multiple to a single first then run filtlong on this (loosing time and disk space in the process)
thanks for any example command that works