Adds:
* Make `mkdocstrings` aware we are using numpy-style docstrings
* Fixes broken link on `index.md` to Python API docs (and added link to
node ones)
* Added examples to various classes.
* Added doctest to verify examples work.
pypi does not allow packages to be uploaded that has a direct reference
for now we'll just ask the user to install tantivy separately
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Co-authored-by: Chang She <chang@lancedb.com>