retain FASTQ format through partitioning
fix extract-partitions to keep FQ if the input was FQ
update setup.py for screed fix
fixed error on empty files
added friendly and informative output to extract-partitions
updated ChangeLog for partition_fq_fix branch
Merge pull request #186 from ged-lab/partition_fq_fix

Fix for partitioning to retain FASTQ format throughout.