feat(examples): Add Gno Package for Markdown Rendering

[thanhngoc541]

Related to #2753

This pull request introduces a new Gno package that utilizes the blackfriday library to render Markdown into HTML.

Supported Markdown Syntax:

• Headers (#, ##, ###, etc.)
• Lists (ordered and unordered)
• Links and Images
• Code blocks and inline code
• Emphasis (bold and italic)
• Blockquotes

func RenderExampleHeader() string {
	input := `
# Heading Level 1
## Heading Level 2
### Heading Level 3
#### Heading Level 4
##### Heading Level 5
###### Heading Level 6
`
	out := runMarkdown(input)
	return out
}

func RenderExampleLists() string {
	input := `
# Unordered List

* Item 1
    * Subitem 1.1
    	* Subitem 1.1.1
* Item 2
    * Subitem 2.1
    	* Subitem 2.1.1


# Ordered List

1. First item
   1. Subitem 1.1
      1. Subitem 1.1.1
2. Second item
   1. Subitem 2.1
      1. Subitem 2.1.1
`

	out := runMarkdown(input)

	return out
}

func RenderExampleLinkAndImage() string {
	input := `
# Link And Image
Here is a [link to VarMeta](https://www.var-meta.com/).
![Gno logo](https://www.var-meta.com/favicon-16x16.png)
`

	out := runMarkdown(input)

	return out
}

func RenderExampleCode() string {
	input := `# Code Block
Here is an inline code example: ` + "`" + `fmt.Println("Hello Gno!")` + "`" + `.

` + "``` go\n" + `func foo() bool {
	return true;
	}
` + "```\n"

	out := runMarkdown(input)

	return out
}

func RenderExampleEmphasis() string {
	input := `# Emphasis
This is **bold** text, and this is _italic_ text.
`
	out := runMarkdown(input)
	return out
}

func RenderExampleBlockquote() string {
	input := `# Blockquote #
> This is a blockquote.

> Here is another blockquote with **bold** and _italic_ text.
`

	out := runMarkdown(input)

	return out
}

func RenderExampleTable() string {
	input := `# Table
| Header 1 | Header 2 |
| -------- | -------- |
| Cell 1   | Cell 2   |
| Cell 3   | Cell 4   |
`
	out := runMarkdown(input)
	return out
}

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[thinhnx-var]

@moul @leohhhn
We are pushing more usage examples to indicate what this package can do.
Could you take a look on this PR and give us review if we are going into right approach or not?

[notJoon]

This package appears to be a port of github.com/russross/blackfriday.

Since the original repository uses a BSD license, you need to maintain the original copyright notice and license terms.

Please add a LICENSE file to the root directory of your project. Specifically, please add a file named 'LICENSE' in the root directory.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.86%. Comparing base (01ee5a9) to head (caf6875).
Report is 35 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2811      +/-   ##
==========================================
+ Coverage   60.84%   60.86%   +0.01%     
==========================================
  Files         563      563              
  Lines       75190    75190              
==========================================
+ Hits        45753    45765      +12     
+ Misses      26068    26058      -10     
+ Partials     3369     3367       -2     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (+0.81%)	⬆️
contribs/gnofaucet	15.31% <ø> (+0.85%)	⬆️
gno.land	67.17% <ø> (ø)
gnovm	65.63% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.08% <ø> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[notJoon]

I have left some improvements, mostly they are slice range check relates. Please check and apply them. Thank you.

+) CI failing. Please run gno mod tidy on the markdown directory.

[notJoon]

How about changing the package name to md or markdown?

[notJoon]

Accessing data[0] when the data slice is empty can cause a runtime panic. I think need to check the length of data to prevent accessing an empty slice.

Suggested change

	data = data[offset:]
	c := data[0]
	data = data[offset:]
	if len(data) == 0 {
	return 0
	}
	c := data[0]

This pattern is also found in other functions (e.g., codeSpan). please check them just for safety.

[notJoon]

It would be good to add slice bound check here as well.

Suggested change

	if data[0] != '#' {
	return false
	}
	if len(data) == 0 || data[0] != '#' {
	return false
	}

[notJoon]

add index range check here

Suggested change

	for data[i] != '\n' {
	for i < len(data) && data[i] != '\n' {

[thanhngoc541]

I have update the pull request follow your comment. Thank for your suggestion!

[leohhhn]

Hey @thanhngoc541 - just like #2947, we don't really want to have a HTML library. The point of the Markdown UI bounty was to have a Go-like way to write markdown, instead of manually concatenating strings. This PR adds a processor that converts that already impractical string concatenation into HTML. We don't intend to have either.

Thank you for your effort, but you can close this PR.