SeqFileIn's readRecords() can load IUPAC Fastq files into e.g. Dna5 StringSets

I added an optional tag to readRecords() to control the alphabet of the input file.

This tag is not strictly necessary for the single readRecord(). In this case, the conversion can be controlled by passing a Iupac target String to readRecord() and then assigning manually an Iupac String to eg. Dna5 String.

I had to assign a default value to TSeqFileInAlphabet because the preceding argument already has a default value. As you noticed, the default value Iupac is never taken here. I had thought to use Nothing instead. This is very ugly... 💩