Use standard FASTQ /1 and /2 suffices in output

Previously readphaser output FASTQ files with paired reads using the suffices ``-1`` and ``-2``, which is quite unusual (and was not recognised by all downstream analysis tools). This change adopts the much more common ``/1`` and ``/2`` convention.

Note that I have not tested this change (it would be great to have a test suite but that is a separate issue), I was altered to this issue by the user of one of my scripts which didn't handle ``-1`` and ``-2`` style naming.