splitting hpc-python into hpc-python and hpc-workflows

[psteinb]

I propose to split the hpc-python in half:

• hpc-python: episode 1 to episode 6 remains where it is

• new hpc-carpentry repository 'hpc-workflows': episode 11 to episode 18

The introduction to snakemake (the second part of hpc-python) is very well done and would offer more effective real estate to focus contributors attention if in an isolated repository. I feel that it is a bit hidden currently, which I believe is a shame.

see also #13