wip: make the python API reference a bit nicer (#162)

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.

.github/workflows/python.yml

@@ -35,6 +35,8 @@ jobs:
         pip install pytest pytest-mock
     - name: Run tests
       run: pytest -x -v --durations=30 tests
+    - name: doctest
+      run: pytest --doctest-modules lancedb
   mac:
     timeout-minutes: 30
     runs-on: "macos-12"