Add assembly_reports2ttl.rb

assembly_reports2ttl.rb creates RDF/turtle triples from NCBI assembly_reports resource files.
 * ftp://ftp.ncbi.nlm.nih.gov/genomes/ASSEMBLY_REPORTS/assembly_summary_refseq.txt
 * ftp://ftp.ncbi.nlm.nih.gov/genomes/ASSEMBLY_REPORTS/All/#{id}.assembly.txt