Add support for ContextHashBasedString algorithm

[Ga11u]

I have updated the package by adding an algorithm based on the paper Linked-Data Aware URI Schemes for Referencing Text Fragments (https://doi.org/10.1007/978-3-642-33876-2_17) to create ContextHashBasedStrings.

I added the algorithm as a subpackage, so it does not interfere with the current structure of the project or its semantics. I added a directory called tools and placed the algorithm inside it.

The algorithm is not integrated with the current code. Therefore, no functionality has been changed. This extension only adds support for creating ContextHashBasedString. I also extended the algorithm, so it can create safer hashes (even more unique).

I also created new test for the algorithm and updated the previous test. Some of the previous tests that used the ContextHashBasedString where not fully compliant with the algorithm. For the previous test, I only changed the URI and created them using the new algorithm. It does not effect the functionaly sice the URI for the ContextHashBasedString must be provided and it is not automaticaly generated

[Ga11u]

There is some problem with the coverage command trying to find the py.test when I create the merge request.
I tried to google it but no idea how to solve it.
All the test pass in my local machine, but cannot run in Git.

This is the error:

Run coverage run --source=pynif -m py.test
  coverage run --source=pynif -m py.test
  shell: /usr/bin/bash -e {0}
  env:
    pythonLocation: /opt/hostedtoolcache/Python/3.9.16/x64
    LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.9.16/x64/lib
    GITHUB_TOKEN: ***
__path__ attribute not found on 'py' while trying to find 'py.test'
Error: Process completed with exit code 1.

Do you have any suggestion?