Inconsistent Markdown rendering: underscores don't render as italics or bold; links within italics or bold fail to render (more issues noted in comments)

[samglover]

Describe the bug

In Markdown, text surrounded by asterisks or underscores should render as italics (single asterisks/underscores) or bold (double).

Both of these strings should render as italics: *italics* _italics_

And these strings should render in italics, with a link:

*See: [Link](https://example.com)*
_See: [Link](https://example.com)_

Both of these strings should render as bold: **bold** __bold__

And these strings should render in bold, with a link:

**See: [Link](https://example.com)**
__See: [Link](https://example.com)__

They render properly in GitHub issues, for example:

italics
italics
See: Link
See: Link
bold
bold
See: Link
See: Link

However, in Memos they do not:

Steps to reproduce

Paste the following into a note, then click Save:

*italics*
_italics_
*See: [Link](https://example.com)*
_See: [Link](https://example.com)_
**bold**
__bold__
**See: [Link](https://example.com)**
__See: [Link](https://example.com)__

The version of Memos you're using

v0.24.0

Screenshots or additional context

No response

[samglover]

Found another one. HTML is valid in Markdown, so I tried <small>See: [Example](https://example.com)</small>. GitHub strips the <small> tags, which is OK: See: Example in GitHub.

Memos is weird:

Not sure what's going on there.

[samglover]

Here's another issue, with blockquote rendering. This should all render as one blockquote:

> This
> 
> should all be
> one blockquote

Here is how GitHub renders it:

This

should all be
one blockquote

Here is what it looks like in Memos:

[johnnyjoygh]

FYI, the markdown syntax of memos is a subset of GFW(GitHub Flavored Markdown), so we will gradually implement other syntaxes based on demand.