Update docs

[charlottekostelic]

Changed:

• changed Retry args in MetadataSession and WorldcatSession to camel case (all args should now be in camel case per #17)
• updated links to OCLC documentation/website per #57
• split index.md into multiple files to allow for multiple pages on https://bookops-cat.github.io/bookops-worldcat (new pages listed below)
• theme of docs: readthedocs > material
• typos in multiple files (I added the Code Spell Checker extension in VS Code which identified a bunch of typos)
• target-version for black in pyproject.toml

Added:

• bytes and BytesIO as types for MetadataSession methods that send MARC record in request body
• mkdocs-material as dev-dependency
• extra.css to customize theme with NYPL colors
• Separate pages in documentation for different functionality:
  • Get Started (start.md)
  • Search WorldCat (search.md)
  • Manage Bibliographic Records (manage_bibs.md)
  • Manage Institution Holdings (manage_holdings.md)
  • Search and Manage Local Data (local.md)
  • Advanced Usage (advanced.md)
• Draft contribution guidelines per #86 (contributing.md, there's still more to add here in a future PR)
• how to add RegistryID as context in WorldcatAccessToken per #83 (this is in the Advanced Usage > WorldcatAccessToken section)
• 1.0 to changelog
• sections in README and docs on changes in version 1.0
• py.typed file and updated pyproject.toml

Removed:

• content from tutorials.md. The page is there as a placeholder and I will update it in a future PR.