Release v0.8.0

[LeeDongGeon1996]

New features are almost ready to be released.

Here's the checklist for releasing v0.8.0:

• [x] Add enough new features, such as new indicators or new params.
• [x] Write corresponding documentation and review. (#231 )
• [x] Add docstrings.
• [x] Update benchmarks.(#233 )
• [x] Final sanity check and code style.
• [x] Release to PyPI.
• [x] Apply release description to tag.