Prisms-jobs

This includes a couple small changes:

- fix bug with "write_submit_script" option
- support slurm "SBATCH --constraint" option
- improve conda build process

Bug fix to enable use from inside containers.

- Make Python2/3 compatible
- Only one environment variable now recognized: ``PRISMS_JOBS_DIR``
- Adds option to write submit scripts to file and then submit by setting ``"write_submit_scripts": true`` in ``PRISMS_JOBS_DIR/config.json``
- Customize ``taskmaster`` submission settings via the ``"taskmaster_job_kwargs"`` setting in ``PRISMS_JOBS_DIR/config.json``

- Fixes python version for argparse dependency in install_requires and requirements.txt in order to conda build

prisms_jobs`` is the next version of [``pbs``](https://github.com/prisms-center/pbs). A rename was deemed necessary after adding Slurm support.

* Online documentation: [https://prisms-center.github.io/prisms_jobs_docs/](https://prisms-center.github.io/prisms_jobs_docs/)
* Re-organizes the job management software dependent portions to be completely in ``prisms_jobs.interface.torque`` and ``prisms_jobs.inteface.slurm``. The appropriate interface is chosen and set in ``prisms_jobs.software``. The choice can be customized or a completely custom interface imported via the ``PRISMS_JOBS_SOFTWARE`` environment variable. See docs for details.
* Fixes things that had broken in ``pstat``, ``psub``, and ``taskmaster``
* Install via `pip` & `conda`
* Set JobDB.update() method to include / not include matching by hostname via the ``PRISMS_JOBS_UPDATE``. See docs for details.