feat: make newline marker configurable

[georglauterbach]

Closes #1015

[eidam-slices]

Hello, I really appreciate your work on making this message optional.
How difficult would be making the whole Flyline's "insert new line" behavior optional?

E.g., I've noticed that even if I call: printf "Hello without new line character",
this is the output: Hello without new line character[flyline inserted newline], and the prompt is printed on a new line. The same thing happens with echo -n.

And sometimes, I just wanna call printf without new line on purpose, and this prevents me.
What do you think?

[HalFrgrd]

With @georglauterbach 's approach, you can set flyline --set-newline-marker "" to not print anything. in this scenario flyline will write on a newline below "Hello without new line character" and not cut it off. flyline basically always needs to start from column 0. I think this is best. I can't imagine users would want to printf without a newline and want flyline to overwrite the output.

[eidam-slices]

Alright, thanks for explaining.
We use Bash a lot at university, so I was a bit confused at first when I noticed that printf always ended up with the prompt on a new line, even when I intentionally didn’t print \n. For a moment I thought I was misunderstanding how printf behaved on my system (I use macOS and teachers are using Linux based distros).
Then I tried it with bash --norc, and it suddenly printed the prompt on the same line as the output. That’s when I realized it was probably related to Flyline.
If I understand correctly, this is basically a design choice / limitation of how Flyline renders the prompt, since it needs to start from column 0.
Thanks for the clarification.

[HalFrgrd]

That makes sense, I see how it can be confusing when you're starting off in bash! Flyline does behave differently than other shells because it has a full TUI as its line editor. I hope that more often than not, when flyline behaves differently, it is for the better :)

[eidam-slices]

Yeah, but still, I guess that Bash w/ Flyline has much much fewer differences from pure Bash, than Zsh or Fish themselves. So Flyline is still perfect solution for me :D

[georglauterbach]

I agree with @eidam-slices, it is a bit weird that flyline actually always inserts the newline, which is unexpected at first sight. Having spent so much time in the terminal, though, I can also confidently say that I consider flyline's behavior an improvement in an interactive session. :) Feel free to ask more if you are curious!