Improve the appereance of the markdown editor

[tupini07]

Hi all 😄 I really love memos, but I find that the markdown editor is lacking, especially when compared against other note apps out there (Obsidian, Logseq, etc). Most offer some sort of in-line highlight to better show what the user is typing. The current editor is basically just an unstyled text-area with keyboard shortcuts.

Now, I know that memos is a young project (and has already accomplished amazing things) but I think it should be possible to leverage some existing open source markdown editor for a quick win (though I don't know how hard it is to fit in the current architecture).

Some projects that come to mind:

• https://github.com/benweet/stackedit
• https://github.com/barelyhuman/mark
• there're also a bunch of other editors we could look at here: https://github.com/mundimark/awesome-markdown-editors

Of course, using a stylized editor means that it might not support or display things in the same way in which memos is currently rendering markdown, which might be a problem for the user. Though from what I've seen most libraries offer both a way to 'edit' and to 'render', so perhaps there's also the question of whether we want to swap the current markdown renderer? The drawback is that it would then happen on the frontend, and it might be harder to add custom styles/tags without editing the underlying library.

Anyway, I just wanted to bring this up as I think it's a very important QoL improvement, and one that might not be that hard to implement!