## Description
The html structure of readthedocs can differ. Currently, the html tag is
hardcoded in the reader, and unable to fit into some cases. This pr
includes the following changes:
1. Replace `find_all` with `find` because we just want one tag.
2. Provide `custom_html_tag` to the loader.
3. Add tests for readthedoc loader
4. Refactor code
## Issues
See more in https://github.com/hwchase17/langchain/pull/2609. The
problem was not completely fixed in that pr.
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Signed-off-by: byhsu <byhsu@linkedin.com>
Co-authored-by: byhsu <byhsu@linkedin.com>
Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>
