20-02-0

Update for 20.02 Support (#182)

* Changed Slurm version to 20.02

* Update pyslurm.pyx for 20.02

* Prepared test environment for Slurm 20.02

* Move mapping of slurm defines to python into seperate folder

  - Makes all (slurm.h, slurmdbd.h, errno.h) "#defines" from slurm headers
    available in Python

* Update slurm.pxd to 20.02

* Update setup.py

- Minimum Cython Version to 0.19
- Remove "staticmethod" mention from scandir function
  - apparently, with recursive functions in a class, "self"
    should be used otherwise the method would constantly break
    when there is a directory inside "pyslurm/"

* Update xmalloc.h, use the correct one for 20.02

* Add new directory jinja2

  - The files in defines/ contains all "#define" variables
    from the slurm headers
  - The *.h.pxd files are automatically created by autopxd2
  - With a simple jinja template, one can easily make changes
    and update the pyslurm/slurm.pxd file
  - It's not really necessary to "automate" this, because the
    SLURM headers only change every major release, so this mustn't
    be done often. And the pyslurm/slurm.pxd file shipped here is already
    complete for 20.02

* Fix -Wsign-compare error

  - Utilize size_t instead of int when dealing with unsigned ints

* Update README

  - bump SLURM Version to 20.05

Co-authored-by: Danny Rotscher <[email protected]>
Co-authored-by: bikerdanny <[email protected]>