Changed single newline without double space at EOL behavior

[YanWittmann]

Thank you for the recent changes!

I had to notice that the renderer suddenly changed it's behavior when rendering text separated in multiple lines.
In the latest update, each line I write is also separated into a new line in the rendered markdown, even without any special formatting.

If I were to compare it to GitHub, the behavior now matches the renderer of GitHub issues & PRs and comments (you can see it with this issue text, where each source line matches a rendered line), where it previously was like the renderer for markdown files when viewed in readmes or other files in a repository (https://gist.github.com/rt2zz/e0a1d6ab2682d2c47746950b84c0b6ee).

Here is a demo, comparing the two versions:

# Demo

First line.
Second line with two spaces at the end.  
Third line with two newlines at the end.

Fourth line.

v0.5.6	v0.8.0

This becomes especially relevant if
I use a formatter that breaks my text
after a certain amount of characters
in each line.

I would expect the old behavior to be correct, or more useful, at least to me.
Or did you change this on purpose? If so, a toggle would be very useful to me. Thanks again!