Adds support for execution in containerized enviroments

[m0rcq]

@gmmoura:

This PR adds support for:

• execution in containerized environments
• adds --base-dir to support explicit output directory for the intermediate files created

The overall aim is to provide isolated running environment in the light of the likely need to execute this workload continuosly to check the zones.

Dockerfile provided is based on pypy3.7 and I can see 20% performance gains vs CPython based 3.7.3.

The documentation has been updated to provide examples and extend the list of available arguments for CycleHunter.py.

I can see @shane-kerr submitted https://github.com/SIDN/CycleHunter/pull/6 with refactored code to support asyncio and improve performance. Pypy supports asyncio, so this possibly will bring an extra performance boost to minimise running times.

[m0rcq]

Thanks for this work, specially the locatization of data and the containerization. I'm likely to change the base image from pypy to python, unless you have a good reason to support pypy. I'll also make changes to install the pip requirements from the requirements.txt file.

@seb-at-nzrs: no specific requirements for pypy, using it as a baseline purely due to performance gains. Thank you for merging the branch.