release 0.8.0

This release adds a few options to htseq-count:

• --nonunique handles non-uniquely mapped reads
• --additional-attr adds an optional column to the output (typically for human-readable gene names)
• --max-reads-in-buffer allows increasing the buffer size when working with paired end, coordinate sorted files

Moreover, htseq-count can now take more than one input file and prints the output with one column per input file.

Finally, parts of the code have been streamlined or modernized, documentation has been moved to readthedocs, and other minor changes.