␤ actually becomes a newline when it shouldn't

[s5bug]

Describe the bug
U+2424 becomes a newline

To Reproduce
Try it out in the demo

Expected behavior
The ␤ character actually shows up in text.

According to Wikipedia:

The Unicode characters U+2424 (SYMBOL FOR NEWLINE, ␤), U+23CE (RETURN SYMBOL, ⏎), U+240D (SYMBOL FOR CARRIAGE RETURN, ␍) and U+240A (SYMBOL FOR LINE FEED, ␊) are intended for presenting a user-visible character to the reader of the document, and are thus not recognized themselves as a newline.

[UziTech]

confirmed:
marked demo
commonmark demo

[UziTech]

It looks like this was introduced to fix "contenteditable" content. #52

Seems to be the same issue with U+00A0 in #897 (comment)

I'm all for removing these substitutions and telling people to substitute these characters in the string before sending it to marked if they need to be substituted.

@styfle @joshbruce should we finally remove these substitutions in v0.8.0?

[styfle]

should we finally remove these substitutions in v0.8.0?

Yes, let's do it 👍

Using contenteditable seems less common than using U+00A0 and ␤ character.

Changing this would also fix #363