ufits v0.7.4

• move the mergereads function to general library
• better reporting for merge illumina reads for both ufits illumina ufits illumina2
• fix for ufits illumina to only require primer if amplicons are longer than the read length. This is to prevent amplicons that are shorter than the read length to be discarded as they are automatically trimmed/merged via usearch -fastq_mergepairs tool (and I can't change this). So the default behavior now is to require a forward primer via --require_primer on setting only if the amplicon length is longer than the read length. Read length is calculated automatically via sampling the first 50 reads, the automatic detection is overruled by the --read_length option