Support parsing input parametres from `pyproject.toml` config

[mbalatsko]

This PR adds possibility to set pip-licences input parameters from pyproject.toml file. The change made to be minimally invasive to project logic:

• All parameters configurable using CLI are configurable using pyproject.toml in the special section for pip-licences tool
• Inputs set in CLI have higher priority than pyproject.toml and can override them
• All different types of parameters parsing from toml and overriding by cli was tested in a separate test

Main motivation: https://github.com/raimon49/pip-licenses/issues/148 and I really love that in modern python packages you could configure all tools in pyproject.toml

[raimon49]

@mbalatsko Thank you! Very interesting suggestion.

Also, your implementation is considerate of existing users and looks very professional.

Toward merging this PR, I think it would be better if the README document has the [tool] table contents of the example TOML file and the specs when loaded.

[mbalatsko]

@raimon49 sure, I completely forgot to add it to README, will do!

[mbalatsko]

@raimon49 please take a look, should be all there

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.13%. Comparing base (b3a3d87) to head (ee26a1c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #200 +/- ## ========================================== + Coverage 99.12% 99.13% +0.01% ========================================== Files 1 1 Lines 457 465 +8 ========================================== + Hits 453 461 +8 Misses 4 4 ```

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[raimon49]

Just shipped v4.5.0 and we can now use the features implemented in this PR. https://pypi.org/project/pip-licenses/4.5.0/