Add Markdown-style shortcuts for inline formats

[thibaudcolas]

Feature. Follow-up to #53

What is the current behavior?

At the moment, only block-level formatting (headings, lists, etc) & horizontal rules have Markdown shortcuts.

What is the expected behavior?

It would be cool to have shortcuts for inline formatting:

this is `code`, *italic*, _italic_, **bold**, __bold__

[thibaudcolas]

I realise now that this might be a bit harder than I had initially envisioned, because inline styles created with those markers shouldn't be sticky (while toolbar ones probably should). See withspectrum/draft-js-markdown-plugin#83 (comment).

[loicteixeira]

Umm that's a tough one. I think there are 2 scenarios to consider:

1. As you type
2. As you edit (e.g. when moving the cursor back to the ~start/~end of a text with inline-style)

In the first case, I would agree that once you "close" the style (with the corresponding Markdown tag), there should be no stickiness. It isn't different from the keyboard shortcuts behaviour (e.g. you press cmd+B to "enable" bold mode as you type, but as soon as you press cmd+B again to "disable" it, the bold style isn't sticky).

In the second case, I think it should be sticky as there would be no indication whether that style was applied via the toolbar or markdown formatting. This is the current behaviour whether you used the keyboard shortcut or the toolbar and markdown should be no different.

FWIW, Google Drive seems to have stickiness but Dropbox Paper doesn't. I can't test with Word.

Edit: I realise that in the as you edit scenario, the style is only sticky at the end of the style, not at the start of it but it might be for another issue.

[thibaudcolas]

Totally agree with @loicteixeira's view above.

I think I found a way to have the best of both worlds, which is to only apply the style after the user enters an extra space character after the closing Markdown tag. For example in Dropbox Paper:

Interestingly, it works differently for the code formatting, which doesn't require the space and never sticks. I'm not sure what to think of that.

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Edit: here's an example where styles are never continued: https://markdown-plugin.spectrum.chat/. While I find it ok personally, I'm pretty sure there are lots of people used to continuing styles (or pressing a shortcut like cmd+B, then typing), so to me subsequent additions of text should continue the style no matter how it was entered.

[thibaudcolas]

Implemented in #187.