Add references to test statistics and cross references

[ami232]

This PR addresses issues #28 and #40.

• It adds references to the docstrings of the test statistics functions. Minor fixes are also made to the docstrings in the stat_tests to unify style, fix typos or fix format.
  • Also, wherever they are mentioned across the documentation, they are cross referenced to the page where they are described.

• Add cross references to md files in docs/api and unify style.

[Matgrb]

Overall looks very good, i left some small comments.

Thanks a lot for the contribution! This will make the package easier to use :)

[Matgrb]

Looks great! thanks for making these changes!