Add args list to cli entry points to facilitate debugging

[davidorme]

This PR closes #107 by:

• Adding the args_list argument to all of the entry point functions and handling that within the function
• Adds simple testing that the entry points CLI and entry points functions can be invoked with '-h' successfully.
• Does some tidying up of shared parser arguments and formatting
• Regenerates the command line usage for the docs.

For further work:

• Extend the basic entry point testing to include local actions (where there is no need to mock remote stuff) #110
• Fix the broken XML generation. #109

[codecov-commenter]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (b7f3235) 67.49% compared to head (39dadd8) 72.08%.

Files	Patch %	Lines
safedata_validator/entry_points.py	80.35%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #108 +/- ## =========================================== + Coverage 67.49% 72.08% +4.58% =========================================== Files 13 13 Lines 3655 3668 +13 =========================================== + Hits 2467 2644 +177 + Misses 1188 1024 -164 ```

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