improved convert_fastaqual_fastq library code

made conversion from fasta + qual -> fastq more readable and
less confusing
further streamlined both directions of conversion
Replaced tests for certain errors

Rather than modify the test code, decided to leave in some "quality
assurance" tests
Removed some line continuations, added file naming function
Added buffering system for multiple file output
Added a tests: utility function, multiple output files

also did a little cleanup (could probably use more)
Merge pull request #661 from adamrp/convert_fastaqual_fastq

Convert fastaqual fastq