Change package name from "gl-rs" to "gl"

When the Cargo package manager gets it's online package list, the package name will be used as the
identifier for the whole project.  Keeping "-rs" while useful for the github repository, will be
redundant in Cargo because all of the projects will obviously be rust projects.
Merge pull request #88 from TyOverby/patch-1

Change package name from "gl-rs" to "gl"