Add version in usage information.

Aaron;
This small patch adds versioning for grabix into the usage. This allows me to check the version with CloudBioLinux and ensure we've got the latest and greatest.

I'm hoping to use this for indexing into bgzipped FASTQ files and need the installed grabix to have the no-header initialization fixes from a couple of weeks ago.

On a semi-related topic, do you know of any good ways to apply this approach to indexing BAMs to split into parts, rather than by location? Is that in your places for grabix?