Improve qsub wrapper support for env vars

Address the following issues:
1A. Notes when the -V option is given and
1B. if -v option without -V then include sbatch option of "--export=none"

2A. Does not try to export environment variables by explicitly setting them in the user's environment before invoking sbatch, but instead
2B. Pass specified env vars using the sbatch --export option

3A. Recognize when qsub -v option given with key name, but no value
3B. Find the appropriate value for the specified key name and export that pair.

4. Update documentation