Nucleotide (from nuccore) and protein (only refseq) of viral origin are downloaded and blast db is created.
Updated functions to start working with proteins.
 is now able to download nucleotides or protein sequences (the latter
from RefSeq).  takes a taxonomy mapping file and blast tsv output (outfmt 6)
and returns the list of organisms.
Improved treatment of blast output.
Huge files are not created anymore, blast output is now parsed much quicker.
This is relevant when a lot of reads are from viruses, as in spiking experiments.