Add checksums to documentation

[jonathan343]

Overview

This PR updates the documentation for this package to include the functions in awscrt/checksums.py.

Testing

Note: Python 3.10 is used to match what is being used in the github action that publishes docs. The existing docs fail with Python 3.12. However, that is outside the scope of this PR.

# Setup a Python 3.10 virtual environment
python -m venv venv
. venv/bin/activate

# Install required dependencies
python -m pip install -r requirements-dev.txt
python -m pip install .

# Generate documentation for `awscrt`
cd docsrc
make html

# View the generated documentation
cd build/html
python -m http.server
# View HTML hosted locally. See screenshots below.

Update: I realized there is also a make-docs.py script. That also worked

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.