Support native colored text in Streamlit

[houfu]

As of version 1.26 of Streamlit, colored text is now supported.

We can add a new markdown style (proposed names: streamlit-red-green and streamlit-red). While I haven't tested it, the final output should look something like this:

The quick brown fox :red[~~jumps over ~~]:red[**walks past **]the lazy dog.

TODO:

• [ ] Add the new styles to output_markdown
• [ ] Write tests
• [ ] Update docs