Add retrieval of genes by gene name and extraction of genomic coordinates for exons

@intronic and @ray1729
Thanks for all the work on this library. This pull request updates to the latest JEnsembl and Clojure versions, and adds support for retrieval of genes by gene name and exon coordinates from transcripts.

Ray, would you be open to merging all of the changes back into the original project? This would help avoid all the separate forks. It's not feature complete by any means but would at least be a single collection of all the work done so far.