Enhance LaTeX rendering in Markdown with support for environments

[rian-dolphin]

This PR improves the KatexMarkdownJS function to provide better LaTeX rendering capabilities within Markdown content. Key enhancements include:

1. Support for LaTeX environments (e.g., equation, align, gather, multline)
2. Separate handling for inline and display math
3. Customizable delimiters for inline and display math
4. Configurable list of LaTeX environments to be treated as display math

Changes:

• Updated KatexMarkdownJS function in fasthtml/js.py
• Added support for processing LaTeX environments
• Improved regex patterns for more accurate inline and display math detection
• Made math delimiters and environment list customizable

Breaking Change:

The katex_tags parameter has been replaced with separate inline_delim and display_delim parameters. Users who previously explicitly specified katex_tags will need to update their code.

Migration guide:

• Old: KatexMarkdownJS(katex_tags='$')
• New: KatexMarkdownJS(inline_delim='$', display_delim='$$')

Minimum working example:

This example demonstrates some environments which failed before this PR and now render properly.

from fasthtml.common import *

hdrs = (KatexMarkdownJS(),)
app, rt = fast_app(hdrs=hdrs)


@app.get("/")
def test():
    content = """
Here is some math $x+y=3$.

Examples of environments:
\\begin{align}
x &= y + z \\\\
a &= b + c + d + e
\\end{align}
and the equation environment:
\\begin{equation}
e = mc^2
\\end{equation}
Some more math using the display style deliminators:
$$
1 \\times 2 = 2
$$
final example
$$1 \\times 2 = 2$$
"""
    return Div(content, cls="marked")

serve()

Edit: attaching a before and after screenshot of the example app above.

[rian-dolphin]

cc: yym68686 as this is related to a previous PR

[jph00]

Great! Some minor requests inline. Also, can you please change the code to use named format params and passing a format dict, e.g. like

print('%(Company)s is a %(Department)s Portal.' 
          %{'Company': "GFG", 'Department': "CS"})

[rian-dolphin]

@jph00 I think those are all addressed!

[jph00]

speedy!