Stac Client IO and Documentation Changes

[GregoryPetrochenkov-NOAA]

This PR resolves the following two issues, #166 #167.

Additions

• Images for README
• Files for continuous notebooks
• tutorials.rst
• cases_stac/test_stac.py

Changes

• 04_EXAMPLE.MD/README.MD/PYPI_README.MD_SPHINX_README: Include continuous and catalog comparison example
• compile_readme_and_arrange_docs.py: Add image sizes for new documents
• SPHINX_TUTORIALS: rewrite after compile
• index.rst: nest tutorials in tutorials section
• compute_continuous_metrics.py: Streamline sentinel values for integer datasets
• loading_datasets.py: Add stac client IO functions