added fxn get_genes (fetches sequence data by genbank ID number), edited get_genes_avail
added back tnrs (taxonomic name resolution service) API methods
base URL just changed for the tnrs service
updated readme
added while loop to tnrs fxn so that repeated calls are made to grab data so that a Sys.sleep call is avoided
added NCBI2R in desc file
added remainder of tests, updated NEWS file